I did a little digging after reading your post. A federal doe site cites 7 gallons of diesel fuel per barrel and 20 gallons of gasoline per barrel. as to the tax, this varies from state to state, many tax both the same. My state of pa taxes diesel 8 cents a gallon higher than gas.
I hadnt been aware of that prior to your post.

I still maintain though that a large scale shift to diesel will overtax the supply chain and drive prices higher, much higher. for most drivers it will mostly be about the cost, not the environment and not the fact that we are financing terrorism
It should not be "diesel vs hybrid". the federal program from the nineties had a target of 80 mpg and were well on the way to meeting it combining diesel and hybrid technology and other improvements developed jointly by the big three. Unfortunately Bush dismantled this early on, believing that more drilling was the answer. Detroit threw away their early lead in developing the car of the future and ceded their future to the Japanese.