The national average price of a gallon of regular unleaded leveled off at $2.81 for the week ending May 7, following steady increases that increased the price more than 12% since  early March.

Gasoline is now 45 cents more expensive than it was a year ago. With the summer driving season on the horizon, prices are expected to move higher at a steadier rate, according to AAA.

"If this past week’s moderate increases are any indicator of what’s to come, the fast rate at which gas prices were increasing may be slowing down," said Jeanette Casselano, AAA spokesperson. "On the week, the national average held steady and 19 state averages remained flat or saw decreases in gas prices. Despite this stability, drivers on the West Coast and in Idaho, Utah and Pennsylvania are paying $3 per gallon."

States with the most expensive gasoline include California ($3.63), Hawaii ($3.63), Washington ($3.32), Alaska ($3.28), Nevada ($3.25), and Oregon ($3.23).

States with the largest yearly increases include Indiana (up 66 cents), California (up 66 cents), Utah (up 63 cents), Arizona (up 60 cents), Hawaii (up 56 cents), Idaho (up 55 cents), and Nevada (up 55 cents).

Meanwhile the average price of diesel increased 1.4 cents to $3.171 per gallon, which is 60.6 cents higher than a year ago.

Related: Gasoline Reaches Highest Point in Nearly Four Years