The purpose of this research is to study oil price deregulation policy; whether it is achieved to the government’s expectation or not. The expectations are that the retail price of oil changed following the world market’s price, to be more competitive in the oil market, and not related to political intervention. The result of the study:- oil price deregulation has been as expected. After the policy has been implemented, the retail price changes of oil will not depend on political decision. The refinery factory and the merchant are able to set price according to the cost. The oil price has been adjusted relative to the world situation. However, the retail price of oil in Thailand will still be delayed in adjusting, in relation to the world market. To increase degree of competition in oil markets. Government pursue a policy of deregulating the market conditions and rules, for example permission to be a merchant (section 6) by no longer demanding the merchant to seek. After the enactment of the policy, the merchant is able to set up margin within the market mechanism. That induces new merchants entering more in to the business. After having used concentration index and size ration, the trend of concentration and the difference of oil business size has been decreased. That showed greater opportunities for greater competition from new merchants. With the keen price competition, there has not been obvious in oil market because of the difference in products and goodwill of the consumer. However, the study concludes that more competition between new merchants who come into the business and the old ones who came before does exist.
