Abstract: Optical gas analyzers are disclosed for analyzing gas samples, including a source of radiation, a gas sample cell through which the radiation passes, a mirror for dividing that radiation into a number of secondary radiation paths for each of the gases in the gas sample which is to be analyzed, with the mirror being arranged so that after a single reflection from the mirror each of the secondary radiation paths is directed to an optical filter which passes a preselected wavelength characteristic of the particular gas in question, and then to a detector for measuring that wavelength characteristic. These optical gas analyzers are preferably used in connection with gas samples which include anesthetic gases, along with CO.sub.2 and N.sub.2 O.