Most travelers still budget a considerable part of their summer vacation towards gas, fully expecting the
typical rise in prices by Memorial Day. Who’s behind this summer conspiracy and why does it occur
seemingly each and every year? The answers may surprise you in that there are legitimate costs
associated with producing an approved fuel that the EPA will allow you to sell in July versus,
say…December.

Because summer heat creates or contributes to the creation of an inversion layer -- an immobile layer of
air that often traps pollutants in the lower atmosphere, the government requires adjustment of the product
fuel mix approved for consumer vehicles during summer use. Atmospheric conditions seem to require the
EPA to consider smog and ozone to be of greatest concern during summer months.
Sumer-grade fuel is marginally more eco-friendly because it evaporates more quickly than those
approved for winter-grade sales. This is due to its different Reid Vapor Pressure (RVP). RVP is the
vapor pressure of gasoline measured at 100 degrees Fahrenheit. A fuel’s RVP is influenced greatly by
the ingredients which are approved to make each particular blend. The EPA is concerned about such
because they believe this evaporation contributes to ozone formation.

Winter-grade fuel uses more butane, with its high RVP of 52 PSI, as an additive and consequently
actually costs less to produce. Butane is inexpensive and plentiful and is attractive in that it has an
octane rating above 90%, almost equal to that of premium gasoline. However, its volatility limits the
amount of butane that can be used in summer-grade gasoline (usually not to exceed 2%). Consequently,
less butane equals higher costs leading to higher prices. It really is a pretty legitimate answer to a
problem many ponder each year.

Winter or Summer-grade, gasoline must have an RVP not to exceed 14.7 PSI (pounds per square inch),
which is normal atmospheric pressure. Otherwise, internal pressure could build up in the tank and the
fuel could boil and evaporate. EPA's standards mandate, depending on which part of the country you are
from, an RVP below 9.0 PSI or 7.8 PSI for summer-grade fuel. Because of these varying RVP
standards, 20 or more types of boutique fuel blends will be sold throughout the U.S. before summer’s
end. Naturally, California has its own particular requirements.

Summer grade fuel is more environmentally friendly because it burns cleaner by using a different blend of
fuel additives (oxygenates). It produces less smog and releases fewer toxic air pollutants. However, it is
also more expensive to produce, partially because refineries have to shut down production each year in
order to switch from one blend to another. Also, more cost is incurred in the summer grade fuel because
it contains less butane and instead uses more pricey additives. Summer blend also provides 1.7%
increased energy content, making it more fuel efficient. Winter grade, conversely, requires increased
RVP in order to prevent the engine from starting hard and running rough during cold weather, achieved
in part by the addition of butane, among the more affordable additives available.

A typical summer-grade gasoline is composed of fluid catalytic cracker gasoline, 40%; straight-run
gasoline (directly from crude oil distillation), 25%; alkylate, 15%; reformate, 18%; and butane, 2%. Wintergrade gasoline obviously contains more butane, which allows prices to fall accordingly.

The EPA defines April to June as the "seasonal gas transition" for fuel production. Refineries begin
summer-blend production by March of each year. By June 1, most have switched to selling summergrade gas. Upstream facilities necessary to fuel pumping stations and the like have until May 1 to
comply. By September, the trend is reversed, and the RVP allowance is again changed.

And the cycle continues…