Wood gas is a fuel gas that can be used for furnaces, stoves, and vehicles. During the production process, biomass or related carbon-containing materials are gasified within the oxygen-limited environment of a wood gas generator to produce a combustible mixture. In some gasifiers this process is preceded by pyrolysis, where the biomass or coal is first converted to char, releasing methane and tar rich in polycyclic aromatic hydrocarbons.
In stark contrast with synthesis gas, which is almost pure mixture of wood gas also contains a variety of organic compound ("distillates") that require scrubbing for use in other applications. Depending on the kind of biomass, a variety of contaminants are produced that will condense out as the gas cools. When producer gas is used to power cars and boats or distributed to remote locations it is necessary to scrub the gas to remove the materials that can condense and clog carburetors and gas lines. Anthracite and coke are preferred for automotive use, because they produce the smallest amount of contamination, allowing smaller, lighter scrubbers to be used.
The first wood gasifier was apparently built by Gustav Bischof in 1839. The first vehicle powered by wood gas was built by T.H. Parker in 1901.
Around 1900, many cities delivered fuel gases (centrally produced, typically from coal) to residences. Natural gas came into use only in the 1930s.
Wood gas vehicles were used during World War II as a consequence of the rationing of fossil fuels. In Germany alone, around 500,000 "producer gas" vehicles were in use at the end of the war. Trucks, buses, tractors, motorcycles, ships, and trains were equipped with a wood gasification unit. In 1942, when wood gas had not yet reached the height of its popularity, there were about 73,000 wood gas vehicles in Sweden,
65,000 in France, 10,000 in Denmark, and almost 8,000 in Switzerland. In 1944, Finland had 43,000 "woodmobiles", of which 30,000 were buses and trucks, 7,000 private vehicles, 4,000 tractors and 600 boats.