Some used oil. In California there was a state law requiring woods equipment and locomotives to burn oil, to reduce the risk of fire, and to promote the well conected oil industry.
Down in the woods of the south, almost all of this stuff was wood fired, as will be the case. limbs, crooked places in the trunks, unmerchanrtable species that were in the way, anything that wouldn't make a good saleable log, got cut up fore firewood to feed the boilers.
At one time I modeled the 1890's 100% of my locomotives were woodburning, As I became more interested in logging my time frame migrated to the late 30's, and I retained the 100% woodburning fleet.
Through exploring operational opportunities with Dr, Tom Our time frame migated backwards to the late 20's, so that we could enjoy the greater operational oportunities presented by the booming peak of operations in our neck of the woods, rather than the slow struggling pace of the last feeble efforts to get the last few logs to the mill and cut up before closing down.
That change of time period has had a lot of unforseen repercusions. Locomotives, cars, and buildings, would all be better maintained. As part of the gradual shopping of my locomotives to clean them up, I am convering some of my road locomotives to coal, in keeping with the general practices of big outfints like mine in this region. The mill switcher will still be a woodburner , having a lot of free fuel in the slabs. Also the woods engines will be woodburners, lots of wood laying around, and labor is cheap.
If there was a coal mine on my RR, that would tip the ballance, and more stuff might be coal fired.
In any case I like the looks of the piles of wood by the boiler.
Bill Nelson