GPA 2377-19 covers the determination of the concentration of H2S and CO2 in Natural Gas using a length of stain tube. The ranges covered is 3 ppmv to 5% by volume H2S and 0.25 to 10% by volume of CO2. The Method as written is applicable to the determination of H2S and CO2 in hydrocarbons and in air. This Standard has seen only reprinting and few revisions since 1977 when it was adopted as a tentative method. It was adopted as a Standard in 1984, revised in 1986 and reprinted in 1988, 1997, 1998 and 1999. The current revision updates some materials used in the procedures which by today's best practices would be found obsolete in terms of what we would use to collect or transport a sample to the stain tube, i.e. gum rubber tubing, etc. The most significant addition to the Standard is a "Cautionary Statement". The intention of the statement is to inform the user that it is critical that manufacturer's instructions be followed implicitly. Each lot of stain tubes is tested by the manufacturer for compliance to stated accuracy and each lot or box of stain tubes quite possibly is slightly different in terms of how they are to be used, i.e. exposure times, indicating colors or contaminants, etc. Further the manufacturer's instructions will state the exponent to be used for multiple or partial testing "pulls" of the pump or if these are allowed at all. This information may vary from lot to lot and from one brand of tube to another. Also of significance is the concept that if high accuracy and repeatability is required and chromatography is not indicated or feasible, there are many portable handheld electronic devices available which operate on low power and are intrinsically safe. Therefore, the user should consider if a length of stain tube is really the best commercially available option based on their situation and requirements.