Non-conventional oil

Non-conventional oil is oil produced or extracted using techniques other than the traditional oil well method. Currently, non-conventional oil production is less efficient and some types have a larger environmental impact relative to conventional oil production. Non-conventional types of production include: tar sands, heavy oil, oil shale, biofuels, thermal depolymerization (TDP) of organic matter, and the conversion of coal or natural gas to liquid hydrocarbons through processes such as Fischer-Tropsch synthesis. These non-conventional sources of oil may be increasingly relied upon as petro motor fuel for transportation when conventional oil becomes "economically non-viable" due to depletion. Conventional sources of oil are currently preferred because they provide a much higher ratio of extracted energy over energy used in extraction and refining processes. Technology, such as using steam injection in tar sands deposits, is being developed to increase the efficiency of non-conventional oil production. (from wikipedia)