Diesel is subject to seasonal demands - more expensive in winter (heating demand), where regular gas is more expensive in summer (temperature issues/summer demand) and diesel has more expensive environmental costs for clean burning. Plus, diesel is more demand sensitive since it is not nearly as widely used as regular gas. The commercial demand can increase with economic activity or increases in demand for commercial use, as well as noncommercial demand can affect its price, so it moves very little. And refinery capacity is more oriented towards gasoline as well as servicing other types of fuels. People cannot think about diesel prices the same way as regular gas, but Jack & Jill Public is largely ignorant of these facts and just thinks it is big oil gouging on diesel because they can't gouge as much on gas.