Steam injection is a common method of extracting heavy oil.

It is considered an enhanced oil recovery (EOR) method and is the main type of thermal stimulation of oil reservoirs. There are different forms of the technology, with the two main ones being Cyclic Steam Stimulation and Steam Flooding. Both are applied to oil reservoirs relatively shallow and contain crude oils, which are very viscous at the temperature of the native underground formation. Steam injection is widely used in the San Joaquin Valley of California (USA), the Lake Maracaibo area of Venezuela and the oil sands of northern Alberta (Canada).

Steam flood, known as a steam drive, wells are used as steam injection wells and other wells are used for oil production.

Two mechanisms are at work to improve the amount of oil recovered. The first is to heat the oil to higher temperatures and to thereby decrease its viscosity so that it more easily flows through the formation toward the producing wells. A second mechanism is the physical displacement in which oil is pushed to the production wells. While more steam is needed for this method than for the cyclic method, it is typically more effective at recovering a larger portion of the oil.

The intent is to reduce the viscosity of the bitumen to the point where gravity will pull it down into the producing well.