I'm not sure i understand how one goes about igniting used motor oil.....it's gonna take a lot more then a "small fire" before you can get enough heat to sustain the fire on motor oil. 

I'm guessing you don't approve of IBC's for hydraulic oil or trifliralin either?  We receive both of those products in them....for that matter we receive lots of other oils in smaller, thinner plastic containers.  We have a couple hundred gallons of hydraulic and motor oil in the shop at any given time.   Everything else stays in cold storage.