Can't help you with the oil but I had a Generac 17000 watt unit that I had hooked to an automatic transfer switch. It also ran on Propane. I had a self-check mode where it started and ran once a week for a few minutes to make sure that the battery was charged and that it would start when needed. I can only tell you one thing for sure, that thing literally guzzled LP. I had it hooked to a 300 gallon propane tank and you could almost see the gauge on the tank dropping when it was running. I had it for a specific purpose and when I killed that project, I ended up selling it. Not sure I'll ever buy another one but if I do, I may go with diesel. Haven't really looked into it.