Fossil fuels

Fossil fuels are hydrocarbons, formed from the remains of organisms such as phytoplankton and zooplankton that have settled in anoxic conditions and been subjected to heat and pressure. Since the beginning of their use en masse at the start of the Industrial Revolution, fossil fuels became humanity's primary fuel source.

Fossil fuels are non-renewable resources however, a fact that became most apparant in the 22nd century. A lack of affordable fuels bit deep into the world economy, causing many economic systems to collapse in on themselves. Although society continued to exist under the auspecies of the United Powers League in the 23rd century, the quest for alternative fuel sources was a pressing issue. It was in this period that a scientist, Doran Routhe, theorized that alternative fuel sources could be found beyond the Solar System. This, and other factors, led to the dispatch of the four supercarriers from Earth in 2270, heading for the outlying world of Gantris VI. Due to a computer malfunction, the ships missed their target and ended up in the Koprulu Sector.

Although Routhe didn't know it, his belief that alternative fuels existed was vindicated by the existance of vespene gas.