Gas prices are rising again.

The national average of a gallon of regular unleaded gas jumped 13 cents last week to $3.71, an eight-month high, according to AAA motor club.

"The primary cause appears to be the oil price, which has marched nearly $4 higher in the past few days to hover near $80 per barrel," the news release said. "As oil accounts for almost 50 percent of the cost of a gallon of gas, higher oil prices usually mean higher pump prices."

This summer's heat wave has also contributed to the rising pump prices, some experts say, as extreme heat prevents refineries from running at full capacity.

“If refineries in your region have lower or falling utilization rates, you’re more likely to see gas prices rise,” said Patrick De Haan, head of petroleum analysis of GasBuddy, a platform that helps people find cheap gas. 

Nationwide, refinery utilization decreased by 0.9 percentage points from last week to 93.6%, De Haan said. Gasoline production fell to 9.5 million barrels per day, and distillate fuel production dropped to 4.8 million barrels per day last week. 

“These percentages show how much of a region’s overall capacity was used to refine oil,” De Haan said. “It’s important to note these percentages because the lower the utilization percentage, the lower output, which has a direct impact on local gasoline prices.” 

GAS PRICES UP:Sticker shock hits pump as heat wave, oil prices push cost to 8-month high

Here's where you can find the most expensive and cheapest gas by state, according to AAA:

States with most expensive gas

1. California: $5.05 per gallon
2. Washington: $4.99 per gallon
3. Hawaii: $4.73 per gallon
4. Oregon: $4.65 per gallon
5. Alaska: $4.41 per gallon
6. Nevada: $4.33 per gallon
7. Utah: $4.11 per gallon
8. Illinois: $4.06 per gallon
9. Idaho: $4.00 per gallon
10. Colorado: $3.97 per gallon

States with cheapest gas

1. Mississippi: $3.33 per gallon
2. Louisiana: $3.44 per gallon
3. Alabama: $3.45 per gallon
4. Kentucky: $3.46 per gallon
5. Ohio: $3.46 per gallon
6. Tennessee: $3.48 per gallon
7. Texas: $3.49 per gallon
8. Arkansas: $3.50 per gallon
9. South Carolina: $3.54 per gallon
10. Oklahoma: $3.58 per gallon