[taildragger]

Gas as in Gasoline or Gaseous aka, Propane, LNG, CNG?

With the Fracking Revolution the latter ones are coming on strong in their own right, as I am sure you have read.

[nascarnation]

Gasoline.
This is small stuff like concrete finishers, etc where the engine cost is a big % of the finished product cost.
The compliant diesels are just too expensive.