When crude oil is drilled and commercially exploited, it carries with it a certain percentage of dissolved low molecular weight gases, which tend to come out of solution at the well-head.

For many years it has been accepted practice to flare off this gas, as it was considered uneconomic to utilise this resource. Other sorts of wells only produce gas, and as this resource depletes, the pressure is reduced. In both cases it will eventually become necessary to install compression, if production is to continue.