An online gas price checker has released a study on which retail gas chains offer the lowest prices.
Gasbuddy.com combed through nearly 35 million individual gas prices and compared each brand's pump offering by zip code come up with the the average price. It then ranked the most competitive stations by state.
Costco topped the Washington state list in 2013, followed by Arco, Fred Meyer, USA Petroleum and Safeway. Costco also topped the list across the U.S., followed by Quik Stop, Fred Meyer and Sam's Club.
Costco's price differential between it and the national average was around 16 cents a gallon.