A method of analyzing the products of the oxidation reaction of o-xylene is described. In this system, the sample passes through a Porapak Q column, to trap the hydrocarbons initially, and then to a 5A molecular sieve column to separate carbon oxides and oxygen and nitrogen. The Porapak Q column is then heated to 220°C to desorb the hydrocarbons; the separation of these is achieved in a 10% SE-52 on Chromosorb W column. The importance of removing water vapor from the hydrocarbons in the latter separation is demonstrated.