Policy Pete has an excellent graph showing energy content of fuels. The numbers are as follows:
(numbers guessed from graph)
Natural gas: 46
Crude oil: 38
Coal: 25
Cattle manure: 15
Firewood: 15
Municipal trash: 10
Oil shale: 4
Baked potatoes: 4
Which is great in graphic form. Basically oil shale has less energy than trash and about the same as baked potatoes.