Gasification is a partial oxidation process whereby a carbon source such as coal, natural gas or biomass, is broken down into carbon monoxide (CO) and hydrogen (H₂), plus carbon dioxide (CO₂) and possibly hydrocarbon molecules such as methane (CH₄).

This mix of gases is known as 'producer gas' or product gas (or wood gas or coal gas, depending on the feedstock), and the precise characteristics of the gas will depend on the gasification parameters, such as temperature, and also the oxidizer used.  The oxidizer may be air, in which case the producer gas will also contain nitrogen (N₂), or steam or oxygen.

Gasification technology can be used for:

• Heating water in central heating, district heating or process heating applications
• Steam for electricity generation or motive force 
• As part of systems producing electricity or motive force 
• Transport using an internal combustion engine.

If the gasification takes place at a relatively low temperature, such as 700ºC to 1000ºC, the product gas will have a relatively high level of hydrocarbons compared to high temperature gasification (see below). As a result it  may be used directly, to be burned for heat or electricity generation via a steam turbine or, with suitable gas clean up, to run an internal combustion engine for electricity generation.

The combustion chamber for a simple boiler may be close coupled with the gasifier, or the producer gas may be cleaned of longer chain hydrocarbons (tars), transported, stored and burned remotely.

A gasification system may be closely integrated with a combined cycle gas turbine for electricity generation (IGCC - integrated gasification combined cycle).

Higher temperature gasification (1200ºC to 1600ºC) leads to few hydrocarbons in the product gas, and a higher proportion of CO and H₂.

This is known as synthesis gas (syngas or biosyngas) as it can be used to synthesize longer chain hydrocarbons using techniques such as Fischer-Tropsch (FT) synthesis.

If the ratio of H₂ to CO is correct (2:1) FT synthesis can be used to convert syngas into high quality synthetic diesel biofuel which is completely compatible with conventional fossil diesel and diesel engines.