Gasoline. All the engines in the LAFD "back in the day" were gasoline engines. Actually, I don't remember just how long they could run before running out of fuel, although I have seen them pumping for 3 or 4 hours at a time. A 7-man engine company plus a captain. Today,, you are lucky to get 4 guys on an engine company in L.A. At a big fire on a chilly night, I used to stand pretty close to these things (with my fingers in my ears), they put out a lot of heat.