Complex sentence: Gasification is a process that converts carbonaceous materials, such as coal, petroleum, biofuel, or biomass, into carbon monoxide, hydrogen, carbon dioxide and methane by reacting the raw material at high temperatures with a controlled amount of oxygen and/or steam.
Split into simpler sentences: Gasification is a process that converts organic or fossil based carbonaceous materials into carbon monoxide, hydrogen, carbon dioxide and methane. This is achieved by reacting the fuel-source at high temperatures with a controlled amount of oxygen and/or steam.