| Type | Description |
| Type 1 | Anaerobic (they do not require oxygen to live); they make CH4 (methane) in anaerobic habitats: bottoms of bogs, lakes, sewage treatment ponds, and digestive tracts of animals. |
| Type 2 | Aerobic (they require oxygen to live); they inhabit extra-salty environments: salt evaporation ponds, the Great Salt Lake, and the Dead Sea. |
| Type 3 | Aerobic; they live in hot, acidic springs, at temperatures of 80°C (176°F) to over 90°C (194°F) and pH < 2! |