Over the past decade, state policies on renewable energy have been on the rise in the U.S., providing states with various options for encouraging the generation of renewable electricity. Two promising policies, the Renewable Portfolio Standard (RPS) and the Mandatory Green Power Option (MGPO), have been implemented in many states but the evidence about their effectiveness is mixed. In this paper, we argue that recognizing the natural, social, and policy context under which MGPO and RPS are adopted is necessary in order to measure their true effectiveness. This is because the context rather than the policy might lead to positive outcomes and there is the possibility for sample bias. When controlling for the context in which the policies are implemented, we find that RPS has a negative impact on investments in renewable capacity. However, we find that investor-owned utilities seem to respond more positively to RPS mandates than publicly owned utilities. By contrast, MGPO appears to have a significant effect on installed renewable capacity for all utilities regardless of the context in which it is implemented. (C) 2011 Elsevier Ltd. All rights reserved.