The usual reason for reserve growth in the US is that the SEC requires reporting of reserves only of production that is possible from wells already drilled. As the field gets drilled out, there is necessarily substantial reserve growth. It's also possible for recovery fractions to grow due to better technology - but this factor is not that large. For example, here's Shell estimating that a variety of new technologies should be able to raise average recovery rates from 30% to 38%. OOIP should only change to the extent that pre-Saudi Aramco either misestimated the depth of the oil layer, the porosity of the rock or the extent of the fields. They'd poked holes all over those fields, meaning they'd have had cuttings of the rock all down the wells, and should have had excellent data on the rock layers and the oil column. The only field of any consequence that Saudi Aramco has discovered since 1979 is the Hawtah trend which is not that big and has very tight rocks. For Mr al-Naimi to be an honest man, pre-Saudi Aramco would have had to screw up by a factor of roughly three (unless we want to argue that recovery rates are going to be exceptionally high, but paradoxically, the remaining four fifths of the oil is hard to produce quickly). I eagerly await HO's explanation of how that kind of misestimation could have happened. Perhaps I'll learn something, but given my other 9 bullet points, I'm feeling like I'm on pretty solid ground.

Yes, indeed, I'm glad you raised that point. A whole lot of technology has been invented since oil peaked in the 70's in the US, and despite that technology being used where it makes sense here in North America, those peaked fields are still declining and new fields are not replacing what was once there.

US domestic oil creaks down year by year on a steady basis.