Way back when I were a young-un, we used straight 30-wt non-detergent oil in the gearbox of well pumps (electric windmill-replacement reciprocating pump jacks) and the gearboxes on windmills too. IIRC, the pumpjacks took about a gallon and a half, the windmills about 2 quarts. The electric pumpjacks had a nasty habit of squirting water into their own oil when the packing gland on the wellhead leaked too much, so you changed it a few times a year (and that packing gland would burn itself up if you didn't let it leak just a little to cool it...) Plus we used it for compressors, electric motors, barn fan bearing journals, the concrete mixer gearbox, chain saw bar oil, other small machines, etc... any application where you don't need hypoid lube and you do NOT want any water to emulsify into the oil (as someone else said, "non combustion" applications). Seems like there weren't many big consumers other than that dang pump but it still got used a LOT from day to day around the place. We never bought it in 5-gallon buckets because we were a tiny little 90-acre plot, but I bet a big thousands-of-acres farm or ranch could burn through a quite a few gallons a year.
