mrmoney - I agree that proven oil reserves are merely ball-park estimates that are often over-stated. However, it is also true that they are often under-stated. Ask any geologist, and he will tell you that the oil business is a very tricky business ("slickest companies on the planet"). When they say they have something big, they may have little or nothing. By the same token, when they say they have little or nothing, they may have something big!
Who's to say that Shell didn't announce a write-down in it's proven reserves in order to re-purchase it's own shares at a better price? The only thing we know for sure, is that the reseves are the same today as they were before the change in the "estimate." I don't think new legislation can make much difference.