Over the $3 Threshold Again

I managed to fill up my gas tank last night before this morning's 11-cent price increase to $3.09/gallon. While that's below the national average of $3.27, I hear pundits saying we'll get to $4/gallon this year. Why?

Reason's Ronald Bailey says it not the old law of supply and demand, because we're driving less and using more fuel-efficient vehicles, while gasoline inventories are at their highest since 1993. So, what's going on? He says we should blame the weak dollar, geopolitical uncertainty, and market speculation.