This study investigates the divestiture of transmission control from vertically-integrated power producers, aimed to maintain non-discriminatory access of the transmission network. I ask whether the vertical separation is sufficient to enhance how efficiently production is allocated among generators (i.e., regional production efficiency). Using a difference-in-difference strategy, I compare the treated region, Southwest Power Pool (SPP), with a control region, where no restructuring activities were implemented. Based on robust empirical results, I fail to find significant market wide evidence of improvement in regional production efficiency associated with the vertical separation of transmission control. However, looking into subgroups of generators, I find mixed evidence of cost savings via reallocation of production resources: (1) coal units are dispatched more efficiently after the restructuring; (2) this is not true for two types of gas units with different combustion technologies and cost efficiency.