Why do gas prices rise and fall? 5 driving factors

Why do gasoline prices go up and down so much across the US, and what causes the changes? Here are five key factors that influence gas prices:

2. The summer premium

Bruce Chambers/AP/File
Traffic jams up on the eastbound 91 freeway near Corona, Calif. Heavy traffic contributes to California's smog problem, particularly in the summer. To improve air quality, the state sticks to cleaner summer blend gas longer than the rest of the country.

Gas stations sell summer blend gas during the hot summer driving season, and revert to cheaper winter blend gas in the winter. Summer blend gas creates less smog – particularly important during warm summers, when more drivers hit the road and travel longer distances.

But that summer blend gas comes at a cost, says Mr. Green: “It can add anywhere from 10 to 15 cents a gallon.”

Most states follow Environmental Protection Agency rules for introducing summer blend in June and phasing it out mid-September. If you’re in California, though, you’re buying the “summer blend” earlier than June and into October – raising the cost of gasoline, but reducing smog in a state historically plagued by air quality problems.

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