This Technical Report specifies a method of measuring the oxidative thermal stability of polyethylene pipe and fitting material in oxygen at typical processing and welding temperatures. It may be used to measure the stability of either raw materials or finished products, and may be taken as an indication of polymer or anti-oxidant performance. The recommended test temperatures of 200 YZ and 210 “C are suitable for adequately stabilized pipe and fitting materials. The thermal stability measured by this method is dependent on test specimen mass and size.