I ran my VW camper on used chip oil for a few months apart from a pinking sound (which you don't get if you mix it 50/50) it smelled like an old chip shop!! but ran perfectly.
I used to buy mine at a so called green garage affair!! you can get two prices, one for road use (tax paid) or one for agricultural use (tax free or reduced) a vast difference in the price. You are not permitted to use the tax free fuel on the road!! so you buy a big stock of agricultural priced fuel(lot of Jerry cans etc) and 5 gallons of duty paid fuel and get a receipt for the duty paid, and then if you are stopped and your tank is dipped you can prove you have paid the duty!! both agricultural fuel and duty paid fuel comes out of the same pump!!
I know!! I'm bad!!