Volunteer use as an alternative service delivery arrangement entails public organizations directly incorporating volunteers in service production through a quasi-employment relationship. However, research evaluating the contributions of volunteer labor to organizational performance are relatively few. This article fills this gap by drawing from two theoretical insights. First, this study tests a linear model based on the traditional human resource management approach of interchangeability in which volunteers constitute a one-on-one substitute for paid employees. Second, this study draws insight from critical mass theory to explore a nonlinear model based on the assumption that the productivity of one volunteer may not be equal to that of one paid employee due to the systematic limitations of volunteer labor. Analyzing a large-N panel dataset of 2,420 local law enforcement agencies in the United States that utilize sworn volunteers with general arrest powers, the findings indicate that an increase in the number of sworn volunteers has a linear negative effect on clearing violent crimes in sheriffs offices. However, the results also indicate evidence of curvilinear effects on clearing violent crimes in police departments. This article suggests the need to account for the systematic limitations of volunteer labor when measuring performance and to explore multiple indicators. This study contributes to theory building and testing by enabling a two-way understanding of the relationship between volunteer involvement and organizational performance in the public sector.