Today marks the first day that many states and cities across the United States begin switching back to “winter gasoline”. Many times you may have heard us here at GasBuddy talking about summer gasoline being a reason for prices to rise, but as we switch away from the more expensive summer blend, prices do the opposite- they drop.
Why? Due to EPA regulations in warmer months to limit ozone and pollution, there are stricter requirements for gasoline everywhere, and requirements in bigger cities where tens of thousands of vehicles drive everyday are even more stringent. Even smaller communities switch to summer gasoline, but a version that isn’t quite the same as what’s used in larger cities.
Effective today- September 16- those rules and requirements from the EPA have eased. Summer gasoline contains blending components that cost more. With the switch back to winter gasoline, cheaper butane is again blended in to reduce the price of gasoline, but adds to volatility of gasoline.
You may soon also notice a small drop in fuel economy. Winter gasoline contains more butane, which costs less, but also evaporates at a quicker rate and is more volatile. The savings that refiners see are passed on to motorists, similar to when motorists see prices rise as refiners produce summer gas each spring. Since the weather grows cooler, the increase in volatility is permissible.
So what’s the difference in gasoline look like? Well, the EPA monitors the Reid Vapor Pressure (RVP)- a measurement of the volatility of gasoline. In summer when weather is warmer, gasoline is more volatile, and RVP must be lower. In winter, or cooler months, gasoline isn’t as volatile, and RVP is allowed to be higher. From June 1 through September 15, most big cities use gasoline that has RVP of 5.7-7.8, while less populated areas used 7.8-9.0 RVP gasoline. Then during the cooler months, RVP rises in some areas to between 13.5-15.0 RVP. The RVP of gasoline depends on where you live.
Normal RVP values look like this:
January-March RVP is 13.5+ in many areas
April-September RVP is 5.7-9.0 in many areas
September-December RVP is 11+ in many areas
As temps warm, air pollution regulations mandate lower RVP numbers. The lower the RVP, the more expensive. Generally, a lower RVP will also indicate a slight increase in fuel economy.
To read on the change from winter to summer gasoline, check out this link to the EPA.
Want to see what type of fuel your area uses in the summer? This map is large and may take several minutes to download over a broadband connection- to see it, click here.
