Pipeline compressors are the preferred choice for the large flow rates required by natural gas transmission applications. Seven different models of pipeline compressors are offered with a choice of axial or conventional opposed inlets. It's aerodynamic performance has been refined to the point where conventional axial inlet compressors offer up to 85% isentropic efficiency and the side inlet RFA36 achieves up to 91%. Each compressor receives custom aerodynamic engineering of the entire gas path. This compressor is also used in gas collection and gas processing plants as export compressors. The majority of compressors at the stations are driven by gas turbines. However, electric drive motors are being used increasingly as an alternative to turbines.