TL;DR: How do you know Ben Kenobi is lying? Because he's opening his mouth.

50% more untruths than truths in ANH.

56% more untruths than truths in all original trilogy.

DISCLAIMERS AND EXPLANATIONS:

The way I interpreted the question was, that the intent was to be uncharitable to Obi-Wan. So that is what I do when scoring.

I deliberadamente pick holes, parse grammar, and do everything else a good lawyer would do in front of judge and jury to show someone as unreliable witness.

COUNTS:

--------------------------------+--------+-------+---------+-------+
                                | IV:ANH | V:ESB | VI:ROTJ | Total |
--------------------------------+--------+-------+---------+-------+
Lies to Luke                    | 40     | 5     | 11      | 56    |
Lies to others                  | 4      | 3     |         | 7     |
False statements (unknowingly)  | 17     | 2.5   | 1.5     | 21    |
Misleading but technically true | 2      |       |         | 2     |
--- TOTAL FALSEHOODS:           |    63  |  10.5 |    12.5 |   86  |
--------------------------------+--------+-------+---------+-------+
Unknown/Unfalsifyable           | 7      | 2     | 2       | 11    |
Commands or questions           | 9      |       |         | 9     |
--- TOTAL UNSCORABLE:           |   16   |     2 |      2  |    20 |
--------------------------------+--------+-------+---------+-------+
Truths to Luke                  | 35.5   | 5     | 9.5     | 50    |
Truths to others                | 4      | 1     |         | 5     |
--- Total Truths:               |   39.5 |    6  |     9.5 |   55  |
--------------------------------+--------+-------+---------+-------+

SCOPE COVERED:

Episodes IV, V and VI SOMENTE PARA. Excluded: Clone Wars; EU/Legends, Disney

Episódio IV

• Let's start with the first moment Obi-Wan opens his mouth. NO, not the first words he says to Luke. He starts out with pretending to be a Krayt Dragon instead of a human. In his defense, Luke is unconscious at that moment. But ala CinemaSins, I'm still dinging him. LIE.

• Rest easy, son, you've had a busy day.

  No he didn't. C-3PO drove the landspeeder. Luke just slept in and then passengered around all day. LIE.

• You're fortunate you're still in one piece.

  Not necessarily. We all know from EU that Sand People/Tuskens do NOT just dismember random Force Users - Sharad Hett was made their war leader. Matter of fact, in "Kenobi" novel, Obi-Wan made "frienemies" with a Tusken leader. MAYBE.

• The Jundland wastes are not to be traveled lightly. Tell me young Luke, what brings you out this far?

  OK, seems to be the truth. Though he himself is traveling them lightly apparently, on foot, even, so DING! LIE.

• Obi-Wan Kenobi... Obi-Wan? Now that's a name I haven't heard in a long time... a long time.

  Well, technically speaking, he heard it 1 second ago. DING!

• Oh, he's not dead, not... not yet.

  TRUE!

• Well of course, of course I know him. He's me! I haven't gone by the name Obi-Wan since oh, before you were born.

  As OP noted, false. He was still called Obi-Wan after Luke was born, and only changed his name (according to Miller's "Kenobi" novel) later on Tatooine. LIE.

• Don't seem to remember ever owning a droid. Very interesting...

  LIE. He owned an astromech in his Jedi fighter in ROTS. Having said that, he's also MISLEADING in principle, since he was implicando that he doesn't know R2-D2. Two dings in one.

• I think we better get indoors.

  VERDADE.

• The Sandpeople are easily startled but they will soon be back and in greater numbers.

  UNKNOWN. We don't have a baseline to test against (nobody ever checked if they DID come back and in greater numbers).

• Quickly, son... they're on the move.

  See above. We don't know if he's lying - we don't see any Sandpeople later in that location but we don't see their absence either.

• That's what your uncle told you. He didn't hold with your father's ideals.

  Actually, Owen agreed with the Jedi large-scale, he never opposed Anakin or New Republic when they met. LIE.

• Thought he should have stayed here and not gotten involved

  LIE. Cleig Lars wasn't married to Shmi yet when Anakin left, and there's no canon example of them - especially Owen - discussing Anakin leaving. There's also no discussion of Anakin's staying or leaving in later canon to shed more light for Obi-Wan.

• Yes, I was once a Jedi Knight the same as your father.

  Half-true. He was a Jedi Knight but became a Jedi master. Let's be charitable and call it TRUE.

• He was the best star-pilot in the galaxy

  VERY questionable (I suspect Jango, or some other Jedi, may have been better) but plausible since we don't have direct proof to the contrary and his Midichlorians - which was what made him such a great pilot - were off the scale. Let's call it a TRUE just to be nice to old man.

• and a cunning warrior.

  Not really cunning. We see what he does in battle in Episode III, his whole rule about traps is "Let's run towards them and spring them". He never executes a single cunning stratagem, tactically or strategically. LIE.

• I understand you've become quite a good pilot yourself.

  Presumably CORRECT, but never actually shown in canon prior to that point. Luke let C-3PO drive. However, in Disney canon, there's zero reason for him to "compreender" that - how would he know?

  NOTA As per @WadCheber's comment, a webcomic shows that. I will investigate and update later. For now, changing to TRUE.

• And he was a good friend. Which reminds me...

  I think he may have called him "friend" to Yoda at the end of ROTS. Let's call that one TRUE.

• I have something here for you. Your father wanted you to have this when you were old enough,

  As OP noted, LIE. His father didn't intend to part with it, and most certainly "died" (from a certain point of view) before discussing his Estate handling plans with Obi-Wan.

• but your uncle wouldn't allow it.

  I don't think it's true, since Obi-Wan never explicitly discussed giving the lightsaber to Luke with Owen in any canon. but need to check the canon where their talking is discussed later. For now, a LIE until better canon source proves me wrong.

• He feared you might follow old Obi-Wan on some damned-fool idealistic crusade like your father did.

  LIE. Anakin never followed Obi-Wan, he followed Qui-Gon, as far as Tatooine was concerned. Obi-Wan didn't even want to take him in the first place! And, as noted above, Obi-Wan didn't discuss that with Owen in canon in the first place, to boot.

• Your father's lightsaber. This is the weapon of a Jedi Knight.

  TRUE... or is it? General Grievous wielded four. Sith wielded them. Pre Vizsla wielded one. So... I'm adding on 1/2 LIE, for not correctly stating "weapon of mostly Jedi Knights, but also some others"!

• Not as clumsy or as random as a blaster.

  LIE. Han is far more effective with a blaster than "random" - pretty much 1 shot 1 kill. Leia's even deadlier, having been trained. And Luke was quite clumsy and random with LS at first. It's not the weapon, it's the wielder who determines this.

• An elegant weapon for a more civilized time.

  I wouldn't call Sith Wars and Old Republic times "civilized" and they already had lightsabers. LIE.

• For over a thousand generations the Jedi Knights were the guardians of peace and justice in the Old Republic.

  Half TRUE, half LIE, because it's an extremely large undercount. KOTOR is ~4000 BBY, which means it's finalmente 10-15 thousand generations. Doing things like that gets you major underpayment penalties from IRS for taxes, I can't be any more lenient than IRS.

• Before the dark times, before the Empire.

  VERDADE.

• A young Jedi named Darth Vader,

  LIE. His name wasn't Darth Vader when he was a Jedi. And he explicitly stopped being a Jedi by the moment Sidious named him Darth Vader.

• ... who was a pupil of mine until he turned to evil

  Well, he was first Qui-Gon's pupil. I'm tempted to call that TRUE to honor Darth Maul's memory. But, actually, I take that back. He wasn't Obi-Wan's Padawan "until he turned to evil" - he was made a Jedi Knight well before then. That stopped the official "pupil" relationship. LIE.

• helped the Empire hunt down and destroy the Jedi Knights.

  VERDADE.

• He betrayed and murdered your father.

  LIE!!!! SPOILER:

  HE DID NOT! HE IS LUKE'S FATHER!

• Now the Jedi are all but extinct.

  Except for a whole bunch found alive in EU. And Kannan in Disney canon. And Ashoka Tano. And Yoda. Granted, Obi-Wan may not have known that, so FALSE, not an intentional lie.

• Vader was seduced by the dark side of the Force.

  Nor really. He was seduced by Palpatine (or should we say Padme? ), without much care about Dark Side at first. ROTS novelization is very explicit about that. I'm tempted to call it a lie since Obi-Wan should know better, but let's pretend he didn't read the novelization and is honestly mistaken. FALSE.

• Well, the Force is what gives a Jedi his power.

  TRUE. No, wait, it's Midichlorians! FALSE! OK, OK, fine, I hate Midichlorians too. TRUTH.

• It's an energy field created by all living things.

  Not true! It's not created by Yuuzhan Vong or Ysalamiri, at the very least. OK, let's pretend Obi-Wan isn't a Jedi Master and doesn't know jack about his galaxy... so merely FALSE.

• It surrounds us ...

  TRUE!

• ... and penetrates us.

  LIE. It doesn't directly "penetrate" you, it interacts with Midichlorians in your cells. You can thank the Maker for that scoring, Obi-Wan.

• It binds the galaxy together.

  There is no canon evidence that it's the Force and not gravity beyond Obi-Wan's statement, so I'll call that "untested theory" instead of "false".

• Now, let's see if we can't figure out what you are, my little friend. And where you come from.

  He knows perfectly well what an R2 astromech unit is. LIE. (Also, R2-D2 was not his friend, he was Anakin's, but that's not as important).

• I seem to have found it. (the message)

  TRUE... maybe. Or R2-D2 simply started playing it because it finally rebooted from the trauma realized his old friend Obi-Wan was there?

• Si devo learn the ways of the Force if you're to come with me to Alderaan.

  LIE. He can come to the Alderaan without learning the ways of the Force. All he needs is a spaceship and a pilot. Or money.

• I need your helpLuke.

  Na verdade não. Luke wasn't any help on the way to Alderaan, or till pretty much the end of Obi-Wan's life for that matter. LIE.

• She needs your help.

  OK, I'll give him that one. She needed lovestruck Luke to go to insane lengths to free her from Imperial confinement. Granted, Obi-Wan didn't know that, because HE told Luke to stick around and wait for him, NOT to go rescue Leia! So, merely FALSE.

  Skywalker Family Reunion: Jailbreaking it!

• I'm getting too old for this sort of thing.

  LIE. Qui-Gon was around his age. Most Jedi were quite successful in their 50's. Yoda kicked &ss at 800 or so.

• That's your uncle talking.

  No, that's Luke talking. He may be agreeing with his uncle, but he's sincere. LIE.

• LUKE: Oh, God, my uncle. Quão confiável é a Olymp Trade? Pensamentos Finais am I ever going to explain this? BEN: Learn about the ForceLuke.

  LIE. How's learning about the Force gonna help Luke обяснявам this to his uncle (who, as per Ben's earlier words, already knows all this anyway!). He's just trying to entice Luke to learn about the Force, under false pretenses (again).

  _{Jedi Mind Trick doesn't apply here: JMT on innocent person without need is against Jedi Code & a path to the Dark Side in canon/EU. Explaining to Owen why Luke missed curfew doesn't fall under acceptable exceptions, Obi-Wan knows that}.

• You must do what you feel is right, of course.

  LIE. Luke just told him that what he feels is right is staying right on Tatooine, and that's decidedly not what Obi-Wan thinks Luke devo fazer.

• They didn't. But we are meant to think they did. These tracks are side by side.

  VERDADE.

• Sandpeople always ride single file to hide there numbers.

  According to EU "Kenobi" novel by Miller, TRUE

  The members of the raiding party had arrived separately, from two different directions. On their final approach, the four had converged, running single-file, in the Tusken manner, until they reached their planned stations behind the northern ridge.

• And these blast points, too accurate for Sandpeople. Somente Imperial stormtroopers are so precise.

  HA-HA-HA-HA-HA-HA!!!! Sure they are. The only people who are "precise" in that film when shooting are Han and Leia and to some extent Luke. LIE.

• Wait, Luke! It's too dangerous.

  Not really. He can sense in the Force if it's too dangerous (shown repeatedly in canon), and at this time, it's NOT too dangerous as STs are long gone. LIE.

• There's nothing you could have done, Luke, had you been there.

  He could have given the Empire the 2 droids, and pretended he's a simple farm boy who knows nothing.

  Now, that may not have been eficaz (since they burned down the Jawas), but he could have done something, nevertheless. Let's be charitable and call this one TRUE, but he's partly guessing here.

• You'd have been killed, too, and the droids would be in the hands of the Empire.

  TRUE, presumably. But it's a counterfactual so impossible to 100% be sure. See above.

• Mos Eisley Spaceport. You will never find a more wretched hive of scum and villainy. We must be cautious.

  LIE. You can find far worse places in the Galaxy, apparently, according to canon. Jabba's palace, for one, so no need to go too far either geographically or by canon.

• You don't need to see his identification.

  OK, that wasn't lying to Lucas, but he's still LYING hiz zhopa off.

  And yes I just used Ender's Game slang in Star Wars question, for those keeping score.

• These are not the droids your looking for.

  Ditto. LIE.

• He can go about his business.

  TRUE! Looks like he doesn't always lie even to Stormtroopers!

• Move along.

  It's a COMMAND.

• The Force can have a strong influence on the weak-minded.

  VERDADEIRO

• You will find it a powerful ally.

  TRUE. Except when JMT Jabba the Hutt :)

• Well, most of the best freighter pilots can be found here.

  Unknown but likely FALSE. Galaxy Far Far Away has millions of worlds, the best pilots are surely diffused through them and don't ALL hang out on Tatooine.

• Only watch your step. This place can be a little rough.

  Actually, it's full of murder, so it's a LOT MORE than "a little" rough. LIE!

• This little one isn't worth the effort.

  Again, not lying to Luke. But lying nonetheless. Any idea how much Anakin Skywalker's son's head is worth to the Imperials?

• Come let me buy you something...

  COMMAND.

• This is Chewbacca. He's first-mate on a ship that might suit our needs.

  I don't recall ever in canon reading that Chewie's position was "first mate". Co-pilot? Yes. FALSE.

• Yes, indeed. If it's a fast ship.

  Starts out telling truth to Han. Promising!

• Should I have? (known about Falcon)

  Can't score, it's a question. N/A

• Only passengers. Myself, the boy, two droids ...

  VERDADEIRO

• ... and no questions asked.

  He allowed Han to ask plenty of questions later! ... like... 1 second later! LIE.

  HAN: What is it? Some kind of local trouble?

• Let's just say we'd like to avoid any Imperial entanglements.

  VERDADE.

• We haven't that much with us. But we could pay you two thousand now, plus fifteen when we reach Alderaan.

  Hard to score. Presumably, he didn't intend to lie and simply made a mistake. BUT!!! Alderaanian "fifteen" never did happen! So FALSE!

• Ninety-four.

  N/A. He's just repeating Han's words.

• Você vai tem de sell your speeder.

  Not really, he doesn't HAVE to. Ben can Jedi-mind-trick someone into giving him 2000. Or win a game of chance like Qui-Gon did before. LIE.

• It will be enough. (about speeder's selling price)

  TRUE. It was enough.

• If the ship's as fast as he's boasting, we ought to do well.

  FALSE. The ship's speed is clearly irrelevant, as the Empire is waiting at their destination. Well he didn't know that, so not a lie, just a mistake.

• How long before you can make the jump to light speed?

  A question, so not a lie. I'm tempted to ding him since he's an experienced pilot himself and ought to know! N/A.

• I felt a great disturbance in the Force... as if millions of voices suddenly cried out in terror and were suddenly silenced.

  VERDADEIRO

• I fear something terrible has happened.

  LIE! He didn't "fear". Jedi don't "fear", it leads to Dark Side!

• You'd better get on with your exercises.

  A command, so N/A

• Remember, a Jedi can feel the Force flowing through him.

  TRUE, I suppose. That's how he and other Jedi are described when doing Forcey things elsewhere in canon.

• Partially (re: "You mean it controls your actions?").

  Actually, the Force doesn't ao controle anyone's actions that we observe in canon, at all. Let's be charitable and call it FALSE, he may not have known the Force intricacies, not being a Sith.

• But it also obeys your commands.

  VERDADEIRO

• I suggest you try it again, Luke.

  Another command. N/A

• This time, let go your conscious self and act on instinct.

  LIE! Jedi don't rely on "instinto", which is something wholly different than "flowing with the Force".

• Your eyes can deceive you. Don't trust them.

  TRUE. You see a Force Ghost of Sebastian Shaw, and the next moment, he turns into Hayden Christiansen. Embarrassing, that is.

• Stretch out with your feelings.

  TRUE. Other Jedi describe it that way too in canon

• You see, you can do it.

  TRUE, Captain Obvious! Of course he can, he just did it!

• In my experience, there's no such thing as luck.

  Seriously? How do you describe Han's Sabbac play then? He's not a Jedi! FALSE! Actually, more than that - it's a LIE: Anakin's landing of the ship in ROTS is very explicitly explained as having elements of "luck"! And Obi-Wan was there:

  And at the same time, he draws power from the Force. He gathers perception, and luck, and sucks into himself the instinctive, preconscious what-will-happen-in-the-next-ten-seconds intuition that has always been the core of his talent.

  For that matter, they didn't even need Anakin's luck! Jar-Jar's luck will suffice in Phantom Menace:

  But a quick glance back revealed that they were lucky for a different reason than they thought. The open sea killer was caught in the jaws of a creature so huge that it dwarfed even the beast it was eating. A long, eel-like hunter with clawed forelegs, rear fins, and a wicked pair of jaws was crunching the sea killer into tiny bits and swallowing it down eagerly.

  A LIE!

• That's good. You have taken your first step into a larger world.

  MISLEADING. Luke "took his first step into a larger world" when he first stepped outside Lars homestead years ago. Or got onto Falcon hours ago to leave Tattoine.

• Destroyed... by the Empire!

  VERDADE.

• It's an Imperial fighter.

  VERDADEIRO

• No. It's a short range fighter.

  TRUE. Incidentally, how the hell does HE know? He wasn't keeping up to date on latest Imperial military tech in his cave on Tatoooine, right? So, accidental truth.

• It'd be as well to let it go.

  TRUE. If they did, they wouldn't have ended up Tarkin's guests.

• It's too far out of range.

  FALSE! He knows nothing about Millenium's souped-up systems and Han proves him wrong when he outruns TIEs later.

• Um lutador that size couldn't get this deep into space on its own.

  FALSE! TIE/advanced was about the same size and had a hyperdrive.

  In Obi-Wan's defense, he had earlier complained in canon about not having hyperdrive and needing a hyperdrive ring on Jedi fighters, so he's being genuine here, not lying.

• That's no moon! It's a space station.

  FALSE! A space station implies estacionário position, and Death Star is by no means stationary.

  It also isn't in orbit, which is a most common context implied by that phrase according to Wikipedia definition.

• Si não pode ganhar.

  FALSE. Yes he can. Later in canon, Luke successfully wins over tractor beams, by blowing up stuff that clutters tractor beam and confuses it.

• But there are alternatives to fighting.

  TRUE, duh

• Leave that to me! (re: tractor beam)

  VERDADEIRO

• Who's the more foolish... the fool or the fool who follows him?

  Too fortune-cookie to be falsifiable. N/A

• Plug in. He should be able to interpret the entire Imperial computer network.

  TRUE. Up to and including reading the bloody map that won't show up for 30 years till Episode VII!!!

• I don't think you boys can help.

  He truly doesn't think so, so TRUE

• I must go alone.

  I'll be lenient and call that TRUE, because he needed Jedi Stealth to get by stormtroopers and Hand and Luke would have effed that stealth up.

• Be patient, Luke. Stay and watch over the droids.

  A command, so N/A. On the other hand... if Luke was patient and stayed, he'd never have freed Leia, so FALSE!

• They must be delivered safely or other star systems will suffer the same fate as Alderaan.

  VERDADE.

• Your destiny lies along a different path than mine.

  Actually... he and his Jedi will be betrayed by his student Kylo Ren. Same path! FALSE!!!!

• The Force will be with you... always!

  FALSE! It won't be with him when he's surrounded by Ysalamiri . Or when he fights Clone "Luuke".

  Even in Disney canon, clearly it wasn't with him when Ben "Whiny" destroyed his Jedi Academy.

• Only a master of evil, Darth.

  His name isn't Darth (and nobody refers to him that way), so LIE!

• You can't win, Darth.

  LIE! Sure he can. Short term, he wins by killing Kenobi. Long term, he wins by killing the Emperor, which Yoda and OB1 couldn't do. Darth Vader FTW!

• If you strike me down, I shall become more powerful than you can possibly imagine.

  I donno, he can imagine quite a bit.... :)

  Seriously, LIE. He doesn't become powerful in any meaningful sense of the word.

  Besides, Darth Vader, being a Sith, surely knows about past Sith Lords who successfully escaped death, and came back to life later during KOTOR times.

• Run, Luke! Run!

  A command, so N/A

• Luke, the Force will be with you.

  TRUE, in general. But we established that it won't be with him "Always", so 1/2 TRUE, 1/2 FALSE.

• Use the Force, Luke.

  A command, so N/A

• Let go, Luke.

  A command, so N/A

• Luke, trust me.

  As we see from the above summary... NO!!! LIE!!! He can't be trusted!

• Remember, the Force will be with you... sempre.

  As we already established, A LIE!

Episódio V

• Luke... Luke.... You will go to the Dagobah system.

  VERDADEIRO

• There you will learn from Yoda,

  TRUE ultimately, but remember, Yoda barely agreed to teach him and almost rejected him. So, FALSE as well, from a certain point of view

• the Jedi Master who instructed me.

  A LIE in the big picture. He was mostly taught by Qui-Gon.

  However, from a certain point of view, all Younglings were taught by Yoda as we see in "Lost a planet, Obi-Wan has" scene from AotC, so it's at least partially true.

• He will learn patience.

  FALSE. No he won't. He will rush off to confront Vader on Bespin and nearly ruin everything.

• Was I any different when you taught me?

  A LIE. As we established, he was taught by Qui-Gon. And when we see him as Padawan, he's quite the opposite, Qui-Gon chastises him for NOT living in the moment and using the Living Force (as opposed to Dead Force he was wielding)

• YODA: You are reckless! BEN: So was I, if you'll remember.

  See above. He wasn't ever reckless, he was the MORE cautious out of Qui-Gon and himself; OR out of Anakin and himself. LIE.

• LUKE: But Han and Leia will die if I don't {go}. BEN'S VOICE: You don't know that.

  TRUE. He doesn't know.

• Even Yoda cannot see their fate.

  TRUE. Yoda couldn't see a Sith Master 2 feet away from him for years. Weak, his Oracle-fu, is.

• But you cannot control it {the Force}. This is a dangerous time for you, when you will be tempted by the dark side of the Force.

  LIE.

  • He will be tempted by the Dark side of the Force all his life, not just this time. Starting earlier (Dark Side Cave on Dagobah), then at Jabba's palace, then on Death Star 2, then in a bunch of places in EU/Legends, too numerous to count

  • Moreover, specifically on Bespin, he was NÃO really tempted by the Dark Side, at least in comparison to other times.

• It is you and your abilities the Emperor wants. That is why your friends are made to suffer.

  True? But wait. His friends are actually made to suffer because Pai wants Luke and his abilities (to kill the Emperor and rule the galaxy together). And the Emperor wasn't the one torturing or even ordering torture. FALSE!

• Luke, I don't want to lose you to the Emperor the way I lost Vader.

  True? Except he lost Anakin, he never had Vader. Technically FALSE. Half each.

• Paciência!

  A command. N/A

• If you choose to face Vader, you will do it alone.

  FALSE. Lando helped him to face Vader, by freeing his friends so they aren't hostages to Vader anymore.

• I cannot interfere.

  LIE. He can force-Ghost in front of Vader and say "Boo!!!" and scare the armored pants off of him. May be he MAY not interfere due to some Force Ghost rules (or that he's not allowed to show Vader he is a Force Ghost), but that's different from "CAN".

• Luke, don't give in to hate -

  Command. N/A

• that leads to the dark side.

  VERDADEIRO

• That boy is our last hope.

  LIE!!! "No. There is another." - Yoda, less than a second later.

Episódio VI

• Yoda will always be with you.

  LIE. He will appear once in a while as a Force Ghost in EU, but that doesn't qualify as "always".

• Your father was seduced by the dark side of the Force.

  LIE. As noted in Episode VI lies, he was seduced by Sidious, NOT by Dark Side (which in itself held little attraction to him based on Episode III novelization)

• He ceased to be Anakin Skywalker and became Darth Vader.

  TRUE. He said so himself.

• When that happened, the good man who was your father was destroyed.

  LIE. He was not a "good man" even before that. He was a creepy pervert, who murdered Tusken kids by the village, married Padme despite knowing it was wrong.

• So what I have told you was true… from a certain point of view.

  LIE. It wasn't true! It was just twisting the facts.

• Luke, you’re going to find that many of the truths we cling to depend greatly on our own point of view.

  Hard to say, but given my own (somewhat extensive knowledge) of EU/Legends and Disney canon, I don't think Luke ever finds "muitos" truths he used to cling to to be "depends" category.

  So I'm rating this 1/2 true, 1/2 false.

• Anakin was a good friend.

  VERDADE.

• When I first knew him, your father was already a great pilot.

  VERDADEIRO

• But I was amazed how strongly the Force was with him.

  VERDADE.

• I took it upon myself to train him as a Jedi.

  LIE. Qui-Gon took it upon himself. Obi-Wan merely did what both Qui-Gon and the Jedi Council told him to do.

• I thought that I could instruct him just as well as Yoda. I was wrong.

  Yoda didn't instruct anyone except 3 year old Padawans and Padawans before Dooku who was his last. Obi-Wan didn't witness that. LIE.

• He’s more machine now than man.

  LIE. He has less than 1/2 machine by volume.

• Twisted and evil.

  OK, gotta agree on that one.

• Si não podes escape your destiny.

  LIE. He CAN very easily escape his destiny, slink off to some remote planet and obiwan the rest of his life there. Or slink off to Dagobah and hide out in Yoda's cave.

• Si devo face Darth Vader again.

  LIE. It's not a "must", it's a "should" or "ought". See above. He has an option of running away.

• Then the Emperor has already won. You were our only hope.

  LIE. Leia was another

• The other he spoke of is your twin sister.

  TRUE. I'm tempted to ding 1/2 a lie, because he could have told him prior to two films of unresolved sexual tension and snogging.

• Hmm. To protect you both from the Emperor, you were hidden from your father when you were born.

  VERDADEIRO

• The Emperor knew, as I did, if Anakin were to have any offspring, they would be a threat to him.

  LIE. There is absolutely no canon information that at the time of birth, the Emperor had any específico thoughts about Anakin's kids. He probably had those thoughts, but neither Obi-Wan nor us, the canon consumers, know of them.

• That is the reason why your sister remains safely anonymous.

  TRUE, I suppose. Thought a good lawyer could twist the "safely" into a lie in front of a jury by taking it out of context.

• Your insight serves you well. Bury your feelings deep down, Luke. They do you credit. But they could be made to serve the Emperor.

  VERDADE.

TL;DR: Analyzing Uma nova esperança only (because I don't have time for more), and using the same quotes as DVK posted, I counted 11 definite lies, 2 arguable statements, 7 statements to which no truth value can be assigned (questions or commands), and 75 statements that are definitely not lies - they may be opinions, even incorrect opinions (though we don't know of too many of those), but they're not counterfactual or misleading. Naturally, all numbers are approximate, because where do you draw the line between one statement and the next?, but this means Obi-Wan lies in ANH no more than 15% of the time.

• [pretending to be a Krayt Dragon]

  Sério?

• "Rest easy, son, you've had a busy day."

  Verdade.

• "You're fortunate you're still in one piece."

  True. ("In one piece" is an idiom meaning "not injured". It is not generally used literally.)

• "The Jundland wastes are not to be traveled lightly."

  Demonstrably true.

• "Tell me young Luke, what brings you out this far?"

  No truth value can be assigned.

• "Obi-Wan Kenobi... Obi-Wan? Now that's a name I haven't heard in a long time... a long time."

  True: 20 years is generally considered a long time.

• "Oh, he's not dead, not... not yet."

  Verdade.

• "Well of course, of course I know him. He's me! I haven't gone by the name Obi-Wan since oh, before you were born."

  Per the OP's stipulations, this is a lie.

• "Don't seem to remember ever owning a droid. Very interesting..."

  If we take this as implying that he doesn't know R2-D2, then this is a lie. If we take this as saying "Hm, I wonder why R2 is pretending to be my property when he knows very well that he isn't", well, it's certainly not a lie.

• "I think we better get indoors. The Sandpeople are easily startled but they will soon be back and in greater numbers."

  Verdade.

• "Quickly, son... they're on the move."

  As far as we know, true.

• "That's what your uncle told you. He didn't hold with your father's ideals."

  I think we don't actually know enough about Owen's opinions to evaluate this statement. However, insofar as Obi-Wan is implying that Owen didn't tell Luke about his father because there was a disagreement between the brothers, that's getting into serious "from a certain point of view" territory. I'd have to call this a borderline lie from Obi-Wan.

• "Thought he should have stayed here and not gotten involved."

  Anakin had already left Tatooine and gotten involved before Owen's dad entered the picture, so there is no way to interpret this as true; this is Obi-Wan further spinning his tale about the disagreeing brothers. LIE.

• "Yes, I was once a Jedi Knight the same as your father."

  True. ("Jedi Knight" is the general term as well as a particular rank. All Jedi Masters are Jedi Knights; not all Jedi Knights are Jedi Masters.)

• "He was the best star-pilot in the galaxy"

  Opinion stated as fact is still opinion: as far as we know, Obi-Wan believed this to be true, so it's not a lie.

• "and a cunning warrior."

  Again, a truly-held opinion is not a lie.

• "I understand you've become quite a good pilot yourself."

  Verdade.

• "And he was a good friend. Which reminds me..."

  Verdade.

• "I have something here for you. Your father wanted you to have this when you were old enough,"

  Mentira.

• "but your uncle wouldn't allow it."

  The films don't give us any information about this subject. I think we can classify it as part of the previous lie, though.

• "He feared you might follow old Obi-Wan on some damned-fool idealistic crusade like your father did."

  Insofar as this is still assigning motivations to Owen which we don't know him to have, I think this is a continuation of the lying.

• "Your father's lightsaber. This is the weapon of a Jedi Knight."

  True. (Other people also using lightsabers doesn't mean they're not Jedi weapons. Americans and Australians speaking English doesn't mean we can't call English the language of the British Isles.)

• "Not as clumsy or as random as a blaster."

  Opinion.

• "An elegant weapon for a more civilized time."

  Opinion.

• "For over a thousand generations the Jedi Knights were the guardians of peace and justice in the Old Republic."

  True. ("Over a thousand generations" includes todos numbers greater than one thousand, not just the ones DVK likes.)

• "Before the dark times, before the Empire."

  Verdade.

• "A young Jedi named Darth Vader, who was a pupil of mine until he turned to evil, helped the Empire hunt down and destroy the Jedi Knights."

  Oy. Certain point of view, indeed. Other than the name, this is all true statements, and even the name is true enough if we don't quibble about the timing... This is a preamble to the biggest lie Obi-Wan tells, but is not, in itself, a lie.

• "He betrayed and murdered your father."

  As DVK said, SPOILER:

  HE DID NOT! HE IS LUKE'S FATHER!

• "Now the Jedi are all but extinct."

  As far as Obi-Wan knows, it's down to him and Yoda, so perfectly true.

• "Vader was seduced by the dark side of the Force."

  Verdade.

• "Well, the Force is what gives a Jedi his power."

  Verdade.

• "It's an energy field created by all living things. It surrounds us and penetrates us."

  True. Obi-Wan is perhaps simplifying a bit, but that's a perfectly valid technique when you're explaining a brand-new concept.

• "It binds the galaxy together."

  No idea what Obi-Wan means here, but at worst, it's a statement of opinion.

• "Now, let's see if we can't figure out what you are, my little friend. And where you come from."

  As before, if we interpret this as implying that he doesn't know R2, then it's a lie. But in actual fact, Ben doesn't know what R2-D2 is atualmente - spy? courier? innocent droid? - nor where he came from.

• "I seem to have found it." (the message)

  Verdade.

• "You must learn the ways of the Force if you're to come with me to Alderaan."

  Lie. Sorta. Ben sincerely believes that Luke needs to learn the ways of the Force, but he's putting in the bit about Alderaan to sweeten the pot, not because it's actually true.

• "I need your help, Luke."

  True: once Obi-Wan decided to re-join the fray, he knew he needed all the help he could get.

• "She needs your help."

  More sweetening of the pot, but true enough when you come right down to it.

• "I'm getting too old for this sort of thing."

  Opinion.

• "That's your uncle talking."

  True: Luke was saying "it's not my problem" because that's what he had been taught all his life. By his uncle.

• LUKE: "Oh, God, my uncle. How am I ever going to explain this?" BEN: "Learn about the Force, Luke."

  Nonsequitur, but true enough. Not a lie, certainly.

• "You must do what you feel is right, of course."

  This is Ben saying what he thinks Luke needs to hear, so it's a lie... from a certain point of view.

• "They didn't. But we are meant to think they did. These tracks are side by side."

  Verdade.

• "Sandpeople always ride single file to hide their numbers."

  True, or at worst, opinion.

• "And these blast points, too accurate for Sandpeople. Only Imperial stormtroopers are so precise."

  I know it's fashionable to laugh at this line, but as one of the best answers on this site points out, Stormtroopers are incredibly precise when they're permitido ser.

• "Wait, Luke! It's too dangerous."

  Opinion.

• "There's nothing you could have done, Luke, had you been there."

  True, or at least well-informed opinion.

• "You'd have been killed, too, and the droids would be in the hands of the Empire."

  True, or at least well-informed opinion.

• "Mos Eisley Spaceport. You will never find a more wretched hive of scum and villainy. We must be cautious."

  Opinion, at worst.

• "You don't need to see his identification."

  Lie. :)

• "These are not the droids your looking for."

  More lies. :)

• "He can go about his business. Move along."

  The minute the stormtrooper says it, it becomes true. Trying to figure out whether it's true before that is making my head hurt.

• "The Force can have a strong influence on the weak-minded. You will find it a powerful ally."

  Bem verdade.

• "Well, most of the best freighter pilots can be found here."

  Why Obi-Wan knows this, we don't know, but have no reason to think he's lying. (He did spend some time on Coruscant being a glorified police officer, so he probably learned a thing or two about identifying what's what and who's who in the criminal world.)

• "Only watch your step. This place can be a little rough."

  Understatement, but not a lie.

• "This little one isn't worth the effort."

  Since Obi-Wan clearly intends to protect Luke at all costs, all that bar patron would gain from said effort would be a fatal lightsaber wound or two. Ben is perhaps making assumptions about how high the guy values his own life, but he's not lying.

• "Come, let me buy you something..."

  True, as far as we can see.

• "This is Chewbacca. He's first mate on a ship that might suit our needs."

  Verdade.

• "Yes, indeed. If it's a fast ship."

  Verdade.

• "Should I have?" (heard about Falcon)

  No truth value can be assigned.

• "Only passengers. Myself, the boy, two droids, and no questions asked."

  Verdade.

• "Let's just say we'd like to avoid any Imperial entanglements."

  Verdade.

• "We haven't that much with us. But we could pay you two thousand now, plus fifteen when we reach Alderaan."

  He's playing fast and loose with someone else's money, but he's not lying: he has no intention to stiff Han, as far as we know.

• "Ninety-four."

  Repeating what was said; no truth value can be assigned.

• "You'll have to sell your speeder."

  True. (The possibility of cheating/stealing the money some other way doesn't mean he was lying about selling the speeder.)

• "It will be enough." (about speeder's selling price)

  Verdade.

• "If the ship's as fast as he's boasting, we ought to do well."

  Verdade.

• "How long before you can make the jump to light speed?"

  No truth value can be assigned.

• "I felt a great disturbance in the Force... as if millions of voices suddenly cried out in terror and were silenced."

  Verdade.

• "I fear something terrible has happened."

  Verdade.

• "You'd better get on with your exercises."

  No truth value can be assigned.

• "Remember, a Jedi can feel the Force flowing through him."

  Verdade.

• LUKE: "You mean it controls your actions?" Ben: "Partially. But it also obeys your commands."

  True, or at least we have no reason to think otherwise.

• "I suggest you try it again, Luke. This time, let go your conscious self and act on instinct. Your eyes can deceive you. Don't trust them. Stretch out with your feelings."

  This is all either true or a statement of opinion; none of it is intended to mislead anyone.

• "You see, you can do it."

  True, since he just did.

• "In my experience, there's no such thing as luck."

  Opinion. It's even phrased as such.

• "That's good. You have taken your first step into a larger world."

  Verdade.

• "Destroyed... by the Empire!"

  Jumping to conclusions, perhaps, but not a lie.

• "It's an Imperial fighter."

  Verdade.

• "No. It's a short range fighter."

  Verdade.

• "It'd be as well to let it go. It's too far out of range. A fighter that size couldn't get this deep into space on its own."

  True, as far as Obi-Wan knows.

• "That's no moon! It's a space station."

  True: he doesn't know the official terminology, but the Death Star certainly isn't a moon, but a man-made construct.

• "You can't win."

  True: in a firefight between the Falcon and the Death Star, there can only be one possible winner, and it's not the Falcon.

• "But there are alternatives to fighting."

  Verdade.

• "Leave that to me!" (re: tractor beam)

  Verdade.

• "Who's the more foolish... the fool or the fool who follows him?"

  Opinion, I guess. Definitely not a lie, in any case.

• "Plug in. He should be able to interpret the entire Imperial computer network."

  Verdade.

• "I don't think you boys can help. I must go alone."

  Opinion and/or true.

• "Be patient, Luke. Stay and watch over the droids."

  No truth value can be assigned.

• "They must be delivered safely or other star systems will suffer the same fate as Alderaan."

  Verdade.

• "Your destiny lies along a different path than mine."

  Demonstrably true.

• "The Force will be with you... always!"

  Kind of a tautology, given that the Force is always with everyone, but still: not a lie.

• "Only a master of evil, Darth."

  Quite true: Anakin never reached Jedi Master status, but Darth Vader has certainly achieved the Sith equivalent of that rank.

• "You can't win, Darth."

  Opinion stated as fact, maybe. Not a lie, in any case.

• "If you strike me down, I shall become more powerful than you can possibly imagine."

  Regardless of the truth value of this statement, Obi-Wan clearly believes it strongly enough to sacrifice his life to it. So about as not-a-lie as is humanly possible.

• "Run, Luke! Run!"

  No truth value can be assigned.

• "Luke, the Force will be with you."

  Opinion, hope, or truth, but not a lie.

• "Use the Force, Luke. Let go, Luke. Luke, trust me."

  No truth value can be assigned.

• "Remember, the Force will be with you... always."

  A tautology maybe, but not a lie.

I'm entirely dissatisfied with the state of the existing answers, so here are the times someone using the 'reasonable person' test would consider Obi-Wan lying/stretching the truth while talking to Luke, in order of the most outright lie/misdirection to the smallest (spoiler alert: there aren't many):

1. When Obi-Wan said that Darth Vader betrayed and murdered Luke's father.

(Darth Vader is Luke's father, previously known as Anakin Skywalker)

2. When Obi-Wan said that Luke's father wanted Luke to have his old lightsaber.

(Anakin never referenced or discussed children of his own--real or desired--while talking to Obi-Wan, though it is likely true that, had Anakin maintained custody of his offspring, he would have helped them construct a lightsaber eventually)

3. When Obi-Wan mentions Luke's uncle Owen as the reason for Luke not receiving the lightsaber sooner and as a person who disagreed with Anakin's involvement in the Clone Wars.

(Owen probably didn't think Anakin should be involved in the clone wars but that's because Owen was a simple moisture farmer (in a family of moisture farmers) who thought everyone should mind their own business.

We don't know exactly what kind of words have been spoken between Obi-Wan Kenobi and Owen Lars since Obi-Wan arrived on Tatooine with baby Luke, so we can't ascertain whether Owen at some point during Luke's infancy/childhood said any of those things to Obi-Wan. Therefore this counts as a stretching of the truth or as misleading Luke, but not as an outright lie.)

4. When Obi-Wan mentions that Luke will need to learn the Force if he's to come with Obi-Wan to Alderaan.

(While this is true based on what Obi-Wan means (coming with him on his journey to defeat Darth Vader and the Emperor), it's a bit misleading because he doesn't mention any of these details. They're probably left out because they would discourage Luke, our reluctant hero, from leaving Tatooine. This is therefore misleading Luke at worst, and true at best)

All other lines Alec Guinness' Obi-Wan said to Luke are either true to the best of Obi-Wan's knowledge, matters of opinion, or otherwise not statements of testable veracity (commands, questions, etcetera).

OBI-WAN: Your father wanted you to have this when you were old enough, but your uncle wouldn't allow it.

Maybe they had a conversation offscreen in time of Clone Wars, when Anakin said "If I will have a son, I wish to give him this lightsaber".

To prevent someone saying "Jedi are not allowed to have children, why would Anakin say it?" - Obi-Wan knew that Anakin and Padme were married as he came to her when he was looking for his former apprentice.