Gas prices have risen 26 cents over the past month -- the state average is $3.91 per gallon. So what's behind the price hikes?

As refineries prepare for the summer driving season, they do their maintenance, which slows down production.

And on the other side of that, they produce the summer blend gas -- a cleaner burning fuel.

"Cleaner burning gasoline does cost more to produce and that cost is being passed along," Patrick DeHaan with GasBuddy.com said. 

DeHaan says gas prices here will continue to climb over the next few months.

"Prices in Sacramento, which stand at $3.75, likely will continue to increase. They likely will get close to $4 or surpass $4," he said. 

However, he expects prices to top out around Memorial Day, and start to come down slightly throughout the summer.

Check out gas prices around Sacramento.