Gasoline prices are likely headed higher in the weeks ahead as the impact of refinery maintenance and outages, particularly in California, trickle through the market ahead of the yearly switch to more expensive summer blends.

Here's a look at how weekly regional gas prices changed in Midwest region last week compared with the week prior.

While prices at the pump are lower than they were at this time last year, fuel costs are still up by about 4 cents per gallon compared to this time last month, per AAA data. The national average