[ReelinRod]

Originally Posted by fishaholic18

So what is new???

Besides higher crude prices? Nothing . . .

Every spring gas goes up 10 - 40 cents just with the change to the summer blend. The price rises most between two important dates . . . May 1st when the first drop in vapor pressure rating is mandated and June 1st when only the lowest vapor pressure rated gas can be in the system . . .

Here is a short but relatively thorough explanation:

There are two key (although not the only) specifications that refiners must meet for gasoline. The gasoline needs to have the proper octane, and it needs to have the proper Reid vapor pressure (RVP). While the octane of a particular grade is constant throughout the year, the RVP spec changes with the seasons.

The RVP is based on a test that measures vapor pressure of the gasoline blend at 100 degrees F. Normal atmospheric pressure varies, but is usually around 14.7 lbs per square inch (psi). Atmospheric pressure is caused by the weight of the air over our heads. If a liquid has a vapor pressure of greater than normal atmospheric pressure, that liquid boils. For example, when you heat a pan of water, the vapor pressure increases until it reaches atmospheric pressure. At that point, the water begins to boil.

In the summer, when temperatures can exceed 100 degrees F in many locations, it is important that the RVP of gasoline is well below 14.7. Otherwise, it can pressure up your gas tanks and gas cans, and it can boil in open containers. Gas that is vaporized ends up in the atmosphere, and contributes to air pollution. Therefore, the EPA has declared that summer gasoline blends may not exceed 7.8 psi in some locations, and 9.0 psi in others. The particulars vary, but key considerations are the altitude and motor vehicle density of a specific location.

The EIA summarizes the key points:

As gasoline evaporates, volatile organic compounds (VOC’s) enter the atmosphere and contribute to ozone formation. Gasoline’s propensity to evaporate is measured by Reid vapor pressure (RVP). In order to control VOC emissions, the Federal Clean Air Act Amendments of 1990 require that all gasoline be limited to an RVP maximum of 9.0 psi during the summer high ozone season, which the Environmental Protection Agency (EPA) established as running from June 1 to September 15. The Act also authorized the EPA to set more stringent standards for nonattainment areas. As a result, EPA limits areas designated as “high volatility non-attainment” to a maximum RVP of 7.8 psi during the high ozone season. Some States elected to require even more stringent restrictions to achieve local clean air goals, and require 7.2- and 7.0-psi gasolines.

Butane, which has an RVP of 52 psi, can be blended into gasoline in higher proportions in the winter because the vapor pressure allowance is higher. There are two advantages in doing this. First, butane is a cheaper blending component than most of the other ingredients. That makes fall and winter gasoline cheaper to produce. But butane also adds to the total gasoline pool, so that means that gasoline supplies increase in the winter as more butane is thrown into the mix. Not only that, but this all takes place after summer driving season, when demand typically falls off. These factors normally combine each year to reduce gasoline prices in the fall (even in non-election years). The RVP is stepped back down to summer levels starting in the spring, and this usually causes prices to increase.

The schedule for this seasonal transition varies somewhat from region to region, but in general is as follows. After allowing vapor pressures as high as 15 psig in the winter, the limit drops on May 1st:

May: 9.0 psig
June – Sept. 15: 7/7.8 psig

More congested areas and hotter areas will tend to have a limit of 7.0 psig, while cooler climates generally opt for 7.8 psig. Some cooler climates don't even require a reduction, and have a 9.0 psig limit throughout the summer.

Refiners will start to pull down their inventory of winter gasoline well in advance of the May 1st deadline. On that date, all gasoline in the system has to meet the stricter requirements. This is a key reason that gasoline starts to become more expensive in the spring.

Or it could just be Bush's fault or oil company greed (as if there is a difference huh? ) . . .

This is the part of gas price volatility that I wish the Dems would take credit for . . . Not that I'm against clean air but all these regulations come at a cost . . .