When Allenby and T.E. Lawrence visit the officers' bar in Cairo, immediately after Allenby says "Shall we go outside?", a 1960s motorized vehicle is briefly visible driving by the distant window in the right-middle portion of the frame.
In his interview of Feisal, Jackson Bentley mentions that "certain influential men" in America want their country to join World War I. However, this conversation occurs after the fall of Aqaba, which was in July 1917; by that time, the US had already been in the war for several months.
During the attack on Aqaba, a Turkish soldier is seen with a Browning M1919 machine gun. Which would not have been in use at the time of the Arabian revolt (1917) and it would not have been used by the Turks.
In the well scene when Lawrence and Ali first meet, Ali uses the water bag of the man he has just killed to hoist up some water, fill Lawrence's cup and drink from it. He then drops the water bag, which clearly falls behind the well and can be heard splashing on the ground, but that sound is immediately followed by a much louder dubbed sound of the water bag hitting the bottom of the well.
When T.E. Lawrence is being escorted across the desert on his way to Faisal's camp, his Bedu guide offers to share his food with him. Lawrence is somewhat reluctant but is anxious to show that, unlike other Brits, he is at one with the desert people. He reaches into the guide's proffered dish and takes a morsel - but with his left hand, and he does it twice. The Bedu shows no reaction, but he should: among the desert Bedouin tribes, who eat by hand, the left is kept away from the food as it is the hand with which they clean themselves after defecating. It could be that the guide is observing another Bedouin custom, that of warm hospitality and unstinting generosity to strangers, and is too polite to mention the gaffe (he would probably be aware that many outsiders do not know of the taboo), but it is more likely that it is a genuine error. Peter O'Toole is left-handed, and though he goes to great lengths throughout the rest of the movie to do things right-handedly (Lawrence was right-handed), this was probably a momentary lapse that no one noticed, or thought to mention.
"When T.E. Lawrence is being escorted across the desert on his way to Faisal's camp, his Bedu guide offers to share his food with him..." etc. Lawrence had traveled the region before the war, and knew custom. He would have taken the food in his stride, and would probably not been as clumsy on a camel as he was initially shown.
When Lawrence is crossing the desert with the prince's 50 men he starts to drift off. He is seen looking at his own shadow on the right side of the camel, but in the next shot the shadow is right under the camel. (See also Revealing Mistake)
When Col. Brighton and T.E. Lawrence are having a discussion after just having destroyed the train carrying some horses, the shadow on Col. Brighton's face changes from covering his entire face when both speakers are shown and the sun is behind him, to appearing only beneath the collar of his shirt when he is the only person in the frame.
As Lawrence approaches the Suez canal from the east, he hears then sees over a dune the ship traveling left to right, obviously north. When he goes atop the dune, the ship is trailing away to the south.
As the Arab Army advances upon the Turkish rear, T.E. Lawrence and Ali look to their right at the thunder of the British artillery shelling the Turkish lines. Since in real life they were on the British right flank, they should have been looking to their left.
On their way to Wadi Rhum and Aqabah Lawrence and his party of 50 have to travel north and cross the Devil's Anvil. Yet, when Gasim is seen walking at sunrise he has the sun to his left and a stretched shadow to his right, meaning he is travelling south.
At several points in the movie, Turkish soldiers are shown using Browning Model 1919A6 .30 caliber air-cooled machine guns. The Browning 1919 first entered service in 1919, too late to have been used in WWI. The Turks would have been using German Maxim machine guns. At other times, they are shown using Short-Magazine Lee-Enfield rifles which were standard issue to the British Empire forces. The Turks would, in all likelihood, have been carrying German Mausers.
Throughout the movie T.E. Lawrence is seen carrying a revolver. The Real T.E. Lawrence had sent for two Colt M1911 pistols in 1914 when a friend was traveling in the US and British pistols were scarce due to WW1. In his letters to this brother he wrote: "The Colt is a lovely pistol. The more I examine it the more I like it. There is a vast gulf between it and the ordinary revolver."
When T.E. Lawrence issues the promissory note to Auda he writes right to left. Many have interpreted this as the film being processed backwards when in fact he is writing Arabic which is right to left.
Further to the change of the shadow position during the "drifting" scene, this shot is of an apparent evening/dusk period where the shadow is almost directly under the camel, revealing it to be a "day-for-night" shot which must therefore have taken place near noon.
The goof item below may give away important plot points.
In the movie, Farraj is mortally wounded by a detonator going off in his clothes, but in The Seven Pillars of Wisdom, T.E. Lawrence writes that Farraj was wounded by a Turk shooting him while riding on his camel.