Associated gases at oil wells are often rich in heavy hydrocarbons (HHC, here denoting hydrocarbons heavier than methane). HHC may cause handling and combustion difficulties as their properties are different from standard natural gas, therefore HHC rich associated gases are often flared or vented, wasting an enormous amount of useable energy and contribute importantly to pollution and emissions of CO2 and other greenhouse gases. A major improvement is to use these gases efficiently in a gas turbine, producing mechanical or electrical power at much lower environmental impact. Another application where HHC rich gases often are abundant is in the refining of natural gas (including liquefied natural gas, LNG, and shale gas). Furthermore, off-gases produced in petroleum refineries or other chemical industry may contain HHC, often in combination with hydrogen which is an even more reactive fuel component than HHC. To address these issues Siemens Industrial Turbomachinery AB (SIT AB), Sweden, has tested the standard DLE combustion systems, used in the engine range 25 to 50 MW, with HHC rich gas. In one experimental campaign, pentane was chosen as a model substance for HHC and mixed with natural gas. In another test campaign, 100% ethane was tested without major adaptations to the engine. The unmodified standard SIT AB DLE gas turbines proved to be very tolerant to the tested HHC rich gases. Both SGT-600 and SGT-700 with DLE combustion system has operated on propane. The SGT-700 will soon also operate commercially on ethane rich gas. The conventional combustion systems have gained extensive experience operating on refinery off-gases and the possibility to use such fuels in the DLE systems is also being explored. Avoid flaring or direct release to the atmosphere of associated gases will reduce both pollution and greenhouse emissions importantly; furthermore, it will increase the efficient use of non-renewable energy resources. Gas turbines in the 25-50 MW power range could, in this way, contribute to reduce the environmental impact of conventional power generation technologies.