I attended a conference last March and in one presentation, it was stated that some economists were estimating that speculation accounted for up to $50 per barrel. At that time
oil was in the $90 range. By July
oil had climbed to a peak of $147 and the US economy was beginning to show signs of a serious down turn. The price of
oil began to slide so if speculators were indeed responsible for a good chunk of the cost, they would have started to get out as there was little chance that oil was going to climb any higher.
By mid 2008, the high price of energy was also starting to have a negative effect on the economies of China, India, etc. Demand began to slide so the price began to follow it downward as per Economics 101.
My own estimate 6 months ago was that oil would fall to about $75 per barrel.
Wayne