Recycled Motor Oil Fuel?! Time and equipment costs make this idea prohibitively expensive for consumers and possibly counter-productive for commercial interests but I can see some viability for government subsidized programs. Nonetheless this article is an interesting and informative read. There's an awful lot of waste engine oil available and frankly, I have no idea what happens with it after I bring it to the local auto parts store to dispose of.

https://usfiltermaxx.com/en/content/9-make-black-diesel