This paper examines the importance of market characteristics in restructured electricity markets. We measure market performance relative to benchmarks that abstract away from market design characteristics but capture important structural elements. Specifically, we estimate market outcomes under an assumption of perfect competition and under an assumption of Cournot competition in three U.S. markets: California, New England, and PJM. These two counter-factual assumptions bound the space of possible static, non-cooperative outcomes. By establishing where actual market outcomes fall within these bounds, we can compare how markets perform relative to the extremes determined by structural factors alone. Our findings suggest that vertical arrangements between suppliers and retailers dramatically affect estimated market outcomes. When we include vertical arrangements in firms' objective functions, Cournot equilibrium prices in both PJM and New England fall dramatically. California did not have such arrangements. After accounting for vertical arranegments, performance in each market relative to Cournot is similar, particularly during hours of peak demand.