Posted in: Commentary,
by Patrick DeHaan on Mar 1, 2010 01:10 PM
Get ready to dig deeper in your wallet as summer gasoline slowly begins to arrive at pumps, starting in the South. As I've highlighted many times on the blog, there are many different blends of gasoline depending on time of year and your location. Not all gasoline is equal- states like California run clean-burning gasoline year round, while lesser populated areas of the country burn Winter blended gasoline and save a few pennies.
With the change slowly beginning with Southern states first, I thought I'd give you some information into what's different about gasoline you purchase in warm weather or warm climates.
First, one of the biggest differences is the RVP (Reid Vapor Pressure) of the gasoline. Winter gasoline made for cooler climates has a higher RVP number- meaning it is more volatile. The higher RVP number means the gasoline in your tank is under more pressure. This is why come warmer months, the RVP number must be lower, or the high pressure could result in the gasoline boiling or evaporating, causing an increase in air pollution.
Second, winter gasoline contains more butane. Butane doesn't burn as clean as other "ingredients" in gasoline, but it is far cheaper to mix into gasoline. With the added butane in winter gasoline, you may notice that fuel economy suffers until the warmer months, when refiners cease using as much butane in each gallon. Butane has the highest vapor pressure of just about any other ingredient, coming in over 50psi, which is why summer gasoline doesn't use as much. If it would, the RVP number would be as high as winter gasoline.
Other reasons for higher prices are added oxygenates. These are also added to summer gasoline to lower the RVP number. Typically, winter gasoline has a RVP number of over 10. Come summer, some areas require gasoline that has a RVP number of 7 (for the most populated cities) or 7.8 (for populated cities in cooler climates). In other areas, the RVP must not exceed 9.
To add in, gasoline prices typically rise in the Spring for a few reasons. First, refiners are shutting production and performing maintenance so facilities run with minimal problem during the summer driving season. Second, with all the different blends of gasoline, refiners must alter their production to start producing many different blends of gasoline. This means that supply of summer fuels is slowly increasing, but supply of conventional fuel (for areas with no pollution requirements on gasoline) drops, resulting in higher prices for everyone, no matter what gasoline you burn. Typically supply and other disruptions are sorted out by the start of the driving season, which is why many times prices will stop rising after Memorial Day.