Measurement of the quality of natural gas requires a variety of instrumentation, only one of which is the gas chromatograph. Contractual requirements frequently define the energy content, relative density, and moisture content of the gas being sold. The sale of natural gas is performed on the basis of the heating value per unit volume of the gas. For these reasons, the industry uses instruments to monitor the quality of the gas at the point of sale or at strategic locations along a pipeline. The following instruments are commonly found in the field and in the laboratory: • Gas Chromatographs • Moisture Analyzers • Gravitometers • Hydrogen Sulfide Monitors • Others