An improved gas analyzer for analyzing the concentrations and amounts of one or more different gases in drilling mud returning from a borehole is disclosed. An oil well drilling rig re-circulates the drilling mud by continuously pumping it through a gas separation means. The gas separation means generally includes a fluid stop, a bubble jar and a dririte chamber in order to separate the gases from the drilling mud. A gas sample from these separated gases can be mixed with a carrier gas and are conveyed to gas analyzing means where the concentration of the different hydrocarbon components of the gases in the mud can be continuously measured.