"[S]tories... about "free oil" from coal pyrolysis, often in reference to a low-temperature ... by ... [≈]80 years ago. Many... accompanied by... conspiracy theories... The , and similar carbonization processes... produce a liquid. Presumably, a... clever accountant could figure out how this... could be "free," provided... markets existed for... large amounts of char and gas produced at the same time, and... could be sold... high enough to compensate for giving away the liquid. Then there's the cost of refining the low-temperature into specification-grade marketable fuel..."