AbstractA new approach is proposed for the maximization of profit by optimal scheduling of machinery. Only one objective function (profit) is used instead of two (availability and cost). The latter approach inevitably resulted in suboptimization. In addition, the "single objective function" approach naturally lends itself to comparisons of efficiency between any preventive maintenance policies. Optimal solutions were found in order to compare the efficiency of the commonly used policies of age and block replacement. Numerical results show that age replacement is always more profitable. Optimal solutions for these two maintenance policies were also found in the specific case where a maintenance repair is superior in quality to a breakdown repair. Finally, the physical law of increasing entropy, applied to the failure rate concept, leads to the conclusion that preventive maintenance should always be considered.