Denver gas prices surged again last week, and one expert said they are “likely to remain volatile” ahead of Memorial Day weekend.

The average price for a gallon of gas in Denver rose 35.3 cents last week to end at $4.62 per gallon, according to a GasBuddy survey of 844 stations across the city. That’s 80.6 cents higher than it was a month ago and $1.59 more than a year ago.

The last time Denver headed into Memorial Day weekend with gas prices close to this high was in 2022, when gas was $4.58 per gallon on May 18.

Nationally, the average cost for a gallon of gas remained mostly flat, finishing at $4.47 per gallon last week, down one cent from last week, according to a GasBuddy survey of 150,000 stations.

The price of diesel nationwide sits at $5.62 per gallon on average, GasBuddy said.

Patrick De Haan, head of petroleum analysis at GasBuddy, said the average national price spent much of last week in slight decline as hopes were high that there could be some diplomatic progress between the U.S. and Iran.

“However, that optimism faded after President Trump’s meeting with China’s Xi Jinping failed to produce a breakthrough on Iran, while renewed warnings toward Tehran have helped push oil prices higher again,” De Haan said in a news release.

De Haan said with global oil inventories trending toward historically tight levels, gas prices are extremely sensitive to geopolitical developments and potential supply disruptions right now.

“As a result, gasoline and diesel prices are likely to remain volatile,” De Haan said. “And with Memorial Day approaching, any sustained increase in oil prices could begin pushing retail fuel prices higher again in the weeks ahead.”

Statewide, the average cost for a gallon of gas was also at $4.62, up 30.2 cents week-over-week, GasBuddy said.

The cheapest station in Denver was selling gas at $4.05 last week, GasBuddy said.

However, there were a handful of billboards turning heads this week around Denver that appeared to be advertising unleaded and diesel for $0.00.

The signs were visible at I-76 and Wadsworth Boulevard, at I-70 and Allison Street, at Champa and 14th streets, and at Speer Boulevard and Kalamath Street.

Turns out the billboards are part of a marketing stunt across 14 U.S. cities by Veloz, an organization promoting electric vehicles.

“As we head into one of the busiest and most expensive driving periods of the year, gas price anxiety is hitting Americans where it hurts, with many experts predicting a national average of $5 per gallon,” Veloz said in a news release about its billboard stunt. “Meanwhile, EV drivers’ gas price is $0.00. This clever billboard execution makes that comparison impossible to ignore.”

Veloz said EV drivers save about $166 per month vs. gas vehicles, which adds up to about $2,000 per year.

Editor’s Note: Due to a reporter error, an earlier version of this story misstated the national average for a gallon of gasoline. The average price is $4.47 per gallon, according to GasBuddy. We regret the error.