I think this thread was started a few years ago, and I remember noticing around that time Diesel briefly became cheaper than regular gasoline. But I don't believe it held.
Comifornia has extra tax on Diesel making it more.
Oregon has a unique method to tax diesel.
I believe diesel pickups pay about the same tax rate as gasoline cars.
Diesel commercial trucks, however, only pay a federal tax and not a state tax on the fuel. However, they pay a "Weight Mile" tax which has to be tracked. I'm pretty sure even out of state trucks get hit with it.
And then there is off road diesel. Few stations sell the red dye diesel at the pump, but sometimes one can get a discount for regular green diesel. However, lately the people at the stations haven't wanted to bother with it. However, there may still be a way to get a tax credit for off road diesel use.
The one station on the opposite side of the city that sold me red dye diesel didn't seem to have much of a discount over the regular stations, likely due to handling and volume. I don't know if they had discounts for large volume purchases.