@docdan - Worldwide demand for diesel fuel - barring conspiracy theories about price manipulation by key players - is the most likely culprit. America is literally exporting boatloads of diesel fuel. This is running up the price at the pump. The world wants our diesel.
The seasonal fluctuation in price is what it is, and has been what it is, for eons. The world wants the fuel that our refineries are producing. Yet our refineries are not efficient producers of diesel fuel (the cracking issue).
The Keystone pipeline isn't about creating lower prices at the pump for Americans. It's about refining more fuel to be exported from this country. Yes, it will create some jobs. But it there's more than a good chance that it won't lower fuel prices. It will, from many reports, increase fuel prices in the Midwest, where there's a currently glut of petroleum.
Here's an article on NPR about US petroleum product exports ....
If we as a country fully embrace the boom in cheap Natural Gas, we will lower the use of Diesel Fuel/Heating Oil, by retrofitting trucks and adding more CNG buses, as well as swapping out furnaces and boilers.
If we go whole hog, this can have a significant impact. The questions then, are: 1) what will we do with all of the "excess" diesel, and 2) will it have an effect on prices at the pump.