Most “On-line” gas chromatographs operate for long periods of time without developing biased or even outright unacceptable measurement. Therefore, most users undertake system- wide performance testing infrequently. But as rising gas prices demand increased scrutiny on measurement data – flow volume, energy content, and often hydrocarbon dewpoint analysis — many measurement staffs may search for better performance testing of GC’s, often for the first time. Others may already have adequate performance testing in place but want to review it for completeness. The following points out various factors to be considered