Diesel is less refined......least it use to be nowadays they may take more steps to refine it, in a sense gas takes more step to get crude to gas, vs crude to diesel. Though supply and demand I suppose, more gas used in this country, thefore its cheaper, though with more diesel cars/trucks/suv's coming I wonder if diesel will increase even more so, or if itll be chaper since they'll be selling more of it. Also taxation......off road diesel is cheaper than gas I believe...ya know the red stuff, which is just diesel thats red.......same stuff.