Commonly referred to as a gas turbine, a modern combustion turbine can operate on a variety of gaseous and liquid fuels. The preferred liquid fuel is No. 2 distillate. With proper treatment, crude and residual oil have been used. Fuel gases range from natural gas (essentially methane) to low-heating-value gases such as produced by gasification of coal or heavy liquids, or as by-product gases from blast furnaces. In fact, most gas turbines today are installed with dual- or multi-fuel capability to take advantage of changes in cost and availability of various fuels. Increased capability to burn high-hydrogen-content fuel gas has also been demonstrated, and the ability to operate on 100% hydrogen for zero carbon dioxide emissions is under development.