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Winter consolation: Gas prices tend to go down

As one who prefers golf to skiing, I get a little glum as the days shorten and cold strengthens. There is one consolation: Gasoline prices tend to drop in winter as oil refineries produce winter blends with more cheap butane in the gas mix.

Gasoline evaporates, and the warmer it is, the more its tendency to emit those polluting vapors. To control this, refineries change the seasonal and geographic amount of butane, which controls gas volatility, that is blended into the gas.

In summer, butane content can be as low as 2 percent. In the colder winter and in the north, more butane can be added to 10-12 percent. This extra volatility helps with cold weather starting. But that same more volatile gas in Phoenix could vaporize back in the fuel pump, causing vapor lock.

The additional low cost butane lowers our winter gasoline’s cost and increases its supply. Couple that with reduced winter demand, and we should see lower prices till spring, which helps a little as we slip and slide on icy streets.

All this has been complicated by the arrival of ethanol, which is also volatile, and requires that refineries reduce butane content, slightly raising gasoline’s cost.

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