This paper presents the results of a study of gross mechanical efficiency of racing wheelchair propulsion. Our subjects displayed maximum gross mechanical efficiencies over 30%. Typically trained runners show efficiencies of approximately 25%. Our results may help to explain why trained wheelchair racers are faster than runners. Our results also indicate that the quality of the racing wheelchair, the appropriateness of the wheelchair for the individual, and the training and skill level of the subject play important roles in determining mechanical efficiency. This would suggest that studies of this nature need to be performed on trained wheelchair users, in appropriate wheelchairs.