Fossil fuel embedded energy is still photosynthetic in origin. Terrestrial plants, on the other hand, tended to form coal and methane. Many of the coal fields date to the Carboniferous period of Earth's history. Terrestrial plants also form type III kerogen, a source of natural gas. There is a wide range of organic, or hydrocarbon, compounds in any given fuel mixture. The specific mixture of hydrocarbons gives a fuel its characteristic properties, such as boiling point, melting point, density, viscosity, etc. Some fuels like natural gas, for instance, contain only very low boiling, gaseous components. Others such as gasoline or diesel contain
Bitumen-based fuel associated with the phenol group of surfactants. The most well known bitumen-based fuel has been developed by Intevep, the Research and Development Affiliate of Petroleos de Venezuela SA (PDVSA), in a collaboration with BP, and is branded "Orimulsion." It is an emulsion of natural bitumen mined from the Orinoco Belt and fresh water. Bitumen-based fuel is currently used as a commercial boiler fuel in power plants in Canada, Japan, Lithuania, and China. Commonly available air pollutant control technology can limit emissions from Orimulsion to levels considered Best Available Control Technology, as defined by the United States Environmental Protection Agency. Bitumen-based