Fuel were present at the sites. As a fuel, wood has remained in use up until the present day, although it has been superseded for many purposes by other sources. Wood has an energy density of 10–20 MJ/kg. Recently biofuels have been developed for use in automotive transport (for example Bioethanol and Biodiesel), but there is widespread public debate about how carbon efficient these fuels are. Fossil fuels are hydrocarbons, primarily coal and petroleum (liquid petroleum or natural gas), formed from the fossilized remains of ancient plants and animals by exposure to high heat and pressure in the absence of oxygen
Synthetic fuel synthetic ammonia, and nitric acid. Nearly one third of the Bergius production was produced by plants in Pölitz () and Leuna, with 1/3 more in five other plants (Ludwigshafen had a much smaller Bergius plant which improved "gasoline quality by dehydrogenation" using the DHD process). Synthetic fuel grades included "T.L. [jet] fuel", "first quality aviation gasoline", "aviation base gasoline", and "gasoline - middle oil"; and "producer gas" and diesel were synthesized for fuel as well (e.g., converted armored tanks used producer gas). By early 1944, German synthetic fuel production had reached more than from 25 plants, including 10 in the