Although a number of studies have demonstrated the importance of the degree of factor utilization in economic analysis, the impact of the durations of utilization in a production function remains largely unknown, particularly in terms of the duration of equipment utilization. Using French data on industrial firms over the period 1989–2001, the authors estimate a Cobb-Douglas production function that accounts for the volumes and durations of factor utilization. They draw on the framework proposed by Blundell and Bond (2000), assuming that serially correlated shocks allow a dynamic representation of the production function, and they choose the system-generalized method of moments as the reference estimation method. Their estimates yield identical elasticities for shifts of work and capital: the increase in output resulting from doubling the number of work teams is equivalent to that from doubling the stock of capital. Finally, they cannot reject the null hypothesis of constant returns to scale in their sample.