It's summer travel season with higher gasoline demand and lower heating fuel oil demand. Low natural gas & LP prices have also temporally reduced fuel oil demand. Sweet light crude oil price is down making diesel cheaper to refine. Just wait until crude oil goes back up. Come the end of summer, some fool stirring up the middle east and someday NG and LP prices will rise. Diesel will once again be more $$$ than gasoline. Since 2006 on average diesel has been more $$$ than gasoline. The past few months is just a brief blip.
The oil companies export a lot of diesel to Europe from the USA. Diesel is and will always will be cheaper to refine. The oil companies probably make more money exporting a gallon to Europe than selling it here. Most gasoline sold in the USA has ethanol in it. Most of that is derived from corn. Ethanol is subsidized by the Government. Ethanol is cheaper than diesel, but it takes about 1.2 gallons of diesel to make 1 gallon of ethanol from seed to fuel pump. This makes no sense and is a waste of taxpayers money. The govt. is good at that. There has been no reason for diesel prices to go up. When they went from Low sulfur diesel (LSD) to ultra low sulfur diesel (ULSD). This change is when the price skyrocketed. The cost to reduce the surfer was minimal. The oil companies just pocketed the cash.