In theory, Stahlman's gas, named in honour of Professor Stahlman, was a source of energy found more than twenty miles below the surface of the Earth. It was believed to be infinitely more powerful than North Sea gas.
Professor Stahlman described the gas as "a vast new storehouse of energy that has lain dormant since the beginning of time". He founded the Inferno Project to drill beneath the Earth's crust in order to tap the gas. Due to insurmountable problems with the project, most noticeably the unintended tapping of Stahlman's ooze and the subsequent transformations of humans into Primords, the project was abandoned. (TV: Inferno) On the Inferno Earth the project ruptured the gas pockets causing a worldwide volcanic cataclysm. (PROSE: The Face Of The Enemy)
In a parallel universe in which the Doctor's exile on Earth did not begin until 1997, research into the possibilities of Stahlman's gas was still an ongoing project, and quite a few people invested in it. Marcus was one such person. (AUDIO: Sympathy for the Devil)