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
Pellet fuel #2 Fuel Oil produces 138,690 BTU. Thus if #2 Fuel Oil delivered costs $1.90/Gal, the breakeven price for pellets is $238.00/Ton delivered. Usage across Europe varies due to government regulations. In the Netherlands, Belgium, and the UK, pellets are used mainly in large-scale power plants. The UK's largest power plant, the Drax power station, converted some of its units to pellet burners starting in 2012; by 2015 Drax had made the UK the largest recipient of exports of wood pellets from the US. In Denmark and Sweden, pellets are used in large-scale power plants, medium-scale district heating systems, and small-scale