WINTER BLENDS LEAD TO LOWER GAS PRICES

Denver, September 17 – This week marks the beginning of the yearly transition to winter-blend fuel. Starting on September 15, retailers can begin selling a blend of gasoline that is less expensive to produce because it does not have to meet the same federal emissions reduction requirements that are required during warmer summer months. AAA Colorado reports the average price for a gallon of regular gasoline in Colorado is $3.59, down $3.67 from a month ago. Some areas of Colorado are experiencing prices as low as $3.53 a gallon.

The switch between the two fuels happens twice a year, once in the fall (to winter-blend) and again in the spring (to summer-blend). The difference between summer- and winter-blend gasoline involves the Reid Vapor Pressure (RVP) of the fuel. RVP is a measure of how easily the fuel evaporates at a given temperature. The more volatile a gasoline (higher RVP), the easier it evaporates.

Winter-blend fuel has a higher RVP because the fuel must be able to evaporate at low temperatures for the engine to operate properly, especially when the engine is cold. If the RVP is too low on a frigid day, the vehicle will be hard to start and once started, will run rough.

Summer-blend gasoline has a lower RVP to prevent excessive evaporation when outside temperatures rise. Reducing the volatility of summer gas decreases emissions that can contribute to unhealthy ozone and smog levels. A lower RVP also helps prevent drivability problems such as vapor lock on hot days, especially in older vehicles.

The US Environmental Protection Agency (EPA) says conventional summer-blend gasoline contains 1.7 percent more energy than winter-blend gas, which is one reason why gas mileage is slightly better in the summer. However, the summer-blend is also more expensive to produce, and that cost is passed on to the motorist. When the switch is made to winter-blend, gasoline prices begin to decline.

AAA Colorado provides more than 600,000 members with travel, insurance, financial and automotive-related services and is a leader and advocate for the safety and security of all travelers.