Among local governments, inter-municipal cooperation is the growing reform; but the literature is silent regarding the determinants of longer-term shared service agreements. We conducted a survey of all local governments in New York State in 2013 to assess the level of sharing across 29 public services. The duration of shared service agreements varies from 1 to 80 years. What explains this difference? Our hierarchical linear model shows that service sharing agreements fall along a cooperation continuum, where cost savings are a determinant of shorter agreements, while the public values of service quality and cross-jurisdictional coordination explain longer-term agreements. We also find that positive past experience with sharing partners increases the duration of sharing agreements. Our analysis lays the foundation for new theories of shared services that build directly from the benefits of improved regional coordination, inter-municipal reciprocity and service quality, not from theories based solely on competition and costs.