Regular unleaded increased 1 cent to $2.84 as the nation's gasoline prices plateaued after several months of increasing prices due to the shift to higher-cost summer-blend gasoline and more unplanned refinery maintenance, especially on the West Coast, according to AAA.

The impact at the pump for commercial fleets may be somewhat muted by the slight increase over year-ago fuel prices, said Jeanette Casselano, AAA spokesperson. The April 22 price reflects the smallest one-week jump since the middle of February, and was 23 cents higher than a month ago.

"While prices have been steadily increasing since March, mostly due to the switchover to summer-blend, the national average is just 8 cents more expensive than this time last year," Casselano said. "So not too much of a sticker shock."

For the week, 30 states saw pump-price increases or decreases of 3 cents or less, Casselano said. Gasoline supply continues to tighten, and remain below levels compared to the same time in the past three years.

"The West Coast is probably seeing the most significant impact based on gas prices increases," Casselano said. "In California, retail prices are over $4 per gallon for unleaded. The states has not seen prices this expensive since 2015. Unplanned and planned maintenance, which has tightened gasoline stock levels, have really driven up gasoline prices in the last few weeks much more than expected."

States with the least expensive gasoline include Alabama ($2.50), Mississippi ($2.51), Louisiana ($2.53), South Carolina ($2.53), Arkansas ($2.53), Texas ($2.57), Oklahoma ($2.59), Missouri ($2.59), Virginia ($2.60), and Tennessee ($2.60).

States with the most expensive markets include California ($4.03), Hawaii ($3.59),Washington ($3.46), Oregon ($3.36), Nevada ($3.34), Alaska ($3.26), Arizona ($3.04), Pennsylvania ($2.98), Illinois ($2.98), and Idaho ($2.92).

Meanwhile, the average price for a gallon of diesel increased 2.9 cents to $3.147, which is 1.4 cents higher than a year ago, according to the U.S. Energy Information Administration.