This paper examines the monopoly power in the gasoline industry during the period of 2003-2010. Direct measure of marginal cost and conduct indicates small market power in the gasoline market and decline in monopoly power over time. These findings do not support the general belief that the gasoline prices have been determined through collusion among a few large refining firms. It suggests that importation from other countries should not only deter collusion among the refining firms but also contribute to the decline of their monopoly power over time.