Denver gas prices climbed back up over $4 per gallon this week and one expert attributed it to three main factors.

The average gallon of gas in the Denver metro area on Friday was selling for $4.11, according to a GasBuddy survey of 844 stations across the city. That’s up 15 cents over the last week and 37 cents higher than a month ago.

It’s the second time gas prices have climbed over $4 in Denver since the start of the conflict in Iran, according to GasBuddy, a fuel price monitoring site.

Patrick De Haan, head of petroleum analysis for GasBuddy, said the major factors for higher prices in Denver are the Iran war, global refining capacity and an upswing in price cycling due to the cost of crude oil.

“While the ongoing U.S.-Iran situation continues to weigh on markets, the story is increasingly less about crude oil and more about global refining capacity,” De Haan said Monday. “The Strait of Hormuz remains closed while continued Ukrainian attacks on Russian refineries further squeeze an already strained supply picture.”

Higher crude oil prices are also resulting in the upswing in the price cycle in the Denver market, De Haan said.

Price cycling is a practice in which gas stations drop their prices to compete with neighboring gas stations until they reach a point where they’re losing money per gallon, then push prices higher to restore profit margins and everyone else follows. Then the cycle begins anew.

Nationwide, the average cost for a gallon at the pump was $4.01 on Friday, according to GasBuddy’s survey of 150,000 gas stations across the country. That was up about 11 cents in the past week and 20 cents in the last month.

“Motorists should brace for a rougher stretch ahead,” De Haan said.