Synfuel, short for synthetic fuel

The noun synfuel derives from the adjective synthetic and the noun fuel. A synfuel is a liquid or gaseous fuel derived especially from a fossil fuel that is a solid (as coal) or part of a solid (as tar sand or oil shale) [1].
Synfuels are considered as alternatives to liquid oil, which—within this terminology—is a natfuel (naturally occurring fossil fuel). Coal, oil shale, and tar sand, which all are low state grade energy resources, can be converted by industrial processes into higher state grade resources with the goal to replace natfuel-oil. However, this is inefficient and environmentally problematic. Douglas Reynolds has discussed the economics of oil alternatives and explains [2]:

Since they [synfuels] start out as low state grades, they require expensive transformations before firms can convert them into liquid or gas that could be used in the oil substitutes EUC [energy utilization chain]. Usually, oil from synfuel is three times as labor-to-energy intensive and 10 times as capital-to-energy intensive as crude oil (Rocks, 1989) [Lawrence Rocks: Fuels for tomorrow. Pennwell Corp., Tulsa, OK, December 1980]. Again we get the entropy subsidy problem, where when fuel prices go up, so do labor and material prices. These input prices in turn cause the labor- and material-intensive synfuels [boldface mine] to cost more than originally expected. Thus, any attempt to estimate the cost of synfuels is automatically an incorrect cost, because it does not nor cannot account for the entropy subsidy problem.

Keywords: etymology, energy, technology, resources, oil substitutes, synthetic fuels

References
[1] www.merriam-webster.com/dictionary/synfuel
[2] Douglas B. Reynolds: The Energy Utilization Chain: Determining Viable Oil Alternative Technology. Energy Sources 2000, 22, pp. 215-226.