Occam's razor strikes again. I hope the problem is as simple as you state. Cause I'm sick of wondering.
I heard a VERY interesting statistic on NPR yesterday. Demand has indeed risen over the last year - by a whopping 1%. Now, it seems to me that the price has risen FAR more than 1%. So, what else is going on? I believe the answer is speculation in the oil markets.
A lot of it has to do with speculation. Don't forget though a weakened dollar means imported raw materials cost much more...