I've been doing a lot of research lately on waste oil forges. They are economical, in that the fuel is free, there's no danger of explosions, and they run as hot or hotter than propane. There's a lot of information out there, and a lot of interest, primarily driven by the increasing unavailability and cost of blacksmithing coal, and the cost of propane, and I guess, by a desire to just do it for fun. From everything I've read, they are inexpensive to build and operate (as compared to propane), and reach scary high temps easily. A well designed oil forge can also use propane, diesel, and of course just about any oil (used auto oil, used cooking oil, home heating oil, etc). I may build one this winter, as the idea interests me. Is anyone else interested in this subject, or even better, is anyone using a oil forge?