This paper analyses the degree of market integration in the retail gasoline markets in the United States after it was completely deregulated in 1981. The monthly average prices of unleaded regular gasoline, excluding taxes, from January 1983 to December of 1998 for five US Petroleum Administration Defense Districts were considered in the analysis. There is evidence of a high degree of market integration in the gasoline markets as evidenced by the Engel and Granger and Johansen cointegration tests, but perfect market integration is rejected in all but a few cases.