Winter gasoline

As one who prefers playing golf to skiing, I get a little glum as the days shorten and the cold strengthens. There is one consolation, however: 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 it tends to emit those polluting vapors. To control this, refineries change the amount of butane based on the season and geography.

The mix helps control gas volatility and is blended into the gas.

In the summer, butane content can be as low as 2 percent. In the fall or winter and up north, more butane can be added — up to 10 to 12 percent.

This extra volatility helps with cold weather starting. But that same more volatile gas in a warm area like Phoenix, Ariz., could vaporize too soon, like back in the fuel pump, causing vapor lock.

The addition of 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. Ethanol is also volatile and requires that refineries reduce butane content, slightly raising gasoline’s cost.