The content of dissolved gases in a working liquid can influence outgassing and system properties. A method is presented for determining the dissolved gas content of oxygen, nitrogen, and carbon dioxide in a hydrocarbon-based liquid using gas chromatography. The sampling facility and routine is presented. Various factors influence the gas content such as the sampling position, the preheating time, and the constancy of liquid temperature. Reaching equilibrium between dissolved gases and atmospheric gases is a slow process, requiring sufficient heating and stirring.