The power section of a positive displacement drill motor (PDM) consists of a steel rotor and a tribe with a molded elastomeric lining (stator). Power section failures are typically due to the failure of the stator elastomer. Stator life depends on many factors such as design, materials of construction, and downhole operating conditions. This paper focuses on the stator failure mechanisms and factors affecting stator life. An analytical method for predicting the effect of various design and operating parameters on the strain slate and heat build-ill, within elastomers is discussed. The effect of parameters such as rotor/stator design, downhole temperature, drilling fluid, stator elastomer properties, motor speed, and motor differential pressure on the stator life is discussed. Nonlinear finite clement analysis is used to perform thermal and structural analysis on the stator elastomer. Data from laboratory accelerated life tests on power section stators is presented to demonstrate the effect of operating conditions on stator life.