[Jonty30]

I think work per unit is a good way to measure efficiency. What is more efficient, 9 units of work per gram or 10 units of work per gram?

[thackney]

Efficiency already has a definition.

If you want to make up your own, why not call it “chair” or “sky” or something else as meaningless.

The amount of energy per unit of weight of a fuel is not the efficiency of the engine that uses the fuel.

[thackney]

What is more efficient, 9 units of work per gram or 10 units of work per gram?

Work is a measurement of energy.

It is interesting that you chose to compare the two by weight, which is a measurement of energy density, not efficiency.

What makes it interesting is that the energy/gram is far higher in Natural Gas, compressed or in liquid, than gasoline or diesel. There is 25% more energy in Natural Gas than the same amount of weight in gasoline. For the same amount of pounds of fuel carried in a vehicle, you would travel more miles running on Natural Gas. It would take up more volume.

Most people don't care how much the fuel weighs in their tank. What most people value is the cost to travel, miles per dollar, rather than miles per kilogram. While gasoline is relatively cheap lately, they have become close in cost. For most of the last few decades, Natural Gas has been cheaper.