On May 2009, the Korean government mandated disclosure of gasolineproduct cost information at the oil company level to induce oil companies tocompetitively reduce the wholesale prices of the gasoline products.Theoretically, the disclosure effect of the wholesale price could be eitherpositive (averaged to the lower level) or negative (averaged to the upperlevel). This study investigates the disclosure effect of the wholesale price,using weekly wholesale price at the oil company level. The results fromranking analysis reveal that the ranking volatilities among oil companiesincreased after the cost information disclosure. Furthermore, the results fromthe various graphs show that price dispersion of the wholesale prices (bothgasoline and diesel) decreased, However, the wholesale pricing regressionresults conclude that the wholesale prices were converged to the upper level,contrary to the expectations of the Korean government.