It's because oil sells slower than gas or diesel. The stuff on the shelves of major auto supply houses and the stuff in the warehouses were stocked with the higher priced oil. Since the sales are not as great as fuel the price will drop slower than those at the pump.
They're not gouging. Just trying to get their investment back. Give it some time. Oil will also get very cheap.
Actually the cost of refining diesel is the same as gas. When the refinery cracks crude, it all comes out of the same tower. The top is gas, a little lower is lighter oils like kerosene, and it gets heavier as it syphoned off, Diesel is about mid tower. Cold tar products are at the bottom.
We used to buy diesel for $.26 a gallon back in the day. Same thing for gas in the cabin cruiser....
You're right. The cost of production plays a big part in the retail price. 20 years ago when crude sold for $50 a bbl, gas prices were below a dollar per gallon. Now we're amazed when it breaks the $2 barrier....
Walmart is so much bigger they buy products by the train load, not the car load. It's called purchasing power....