CHICAGO (CBS) — If you’ve filled your tank in the past couple days, you’ve probably noticed a sudden spike in gas prices.

“It’s going to certainly be some pain at the pump for the next couple of weeks,” said Patrick DeHaan, senior petroleum analyst at GasBuddy.com. “By next week, Chicago citywide average could be 15 to 20 cents per gallon higher.”

The reason is the annual switch to more expensive summer blend gasoline, combined with refinery problems over the weekend.

“BPs Whiting, Indiana, refinery suffering what was called a catastrophic failure; ExxonMobil’s facility in Joliet also going down over the weekend; it’s led to concerns about supply, especially during this time when we begin transitioning to that summer blend,” DeHaan said.

DeHaan said he expects the spike in gas prices will be just a blip on the radar.

“This is temporary, and we’re witnessing prices for oil falling back again. After these refinery issues are sorted out, after the summer blend switchover is done, there will be a stronger relationship again between oil and gas prices,” he said. “Gas prices, I would say that by early- to mid-May, will start receding. In fact, summer’s looking very good.”

Even with the sudden rise in prices, the average price of a gallon of gas in the Chicago area is about $2.50, still more than $1 lower than this time last year.