as stated above, use weight instead of volume. The most convenient method for me is Gallon Gas Equivalent (GGE)
Gasoline gallon equivalent - Wikipedia, the free encyclopedia
Look how diesel shows up there, far above any other common fuel. It does indeed contribute to approximately 10% of the economy difference between a petrol and a diesel engine. The rest is due to the better efficiency of the diesel cycle.
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2007 Dodge Ram 3500 SRW 4x4 with 6MT
2003 TDI Beetle
2002 TDI Beetle
currently parked - 1996 Dodge 2500 Cummins Turbodiesel
Custom cab, auto, 3.55 gears