AAA Chicago is saying that refinery problems in Illinois and Indiana are behind gas price increases that took the cost to more than $4 a gallon in the Chicago area, according to the State Journal Register.

According to IllinoisGasPrices.com, the cheapest gas you’ll find in Channahon is $4.09 at Casey's General Store and at the Mobile on Yellow Pine and Eames Street. You can save ten cents by driving to Minooka. In Minooka, the Marathon on Twin Rail Drive has gas for $3.99.

Nationwide, gas prices have risen from an average of 3.32 per gallon of regular to $3.53 per gallon of regular in the last month, according to AAA.

"Illinois, Indiana and states in the Midwest have seen prices rise since last week due to production issues at the BP refinery in Whiting, Ind. and the Citgo refinery in Lemont," Beth Mosher, director of public affairs for AAA Chicago said in a news release. "With the supply from these refineries impacted, and the associated increase in wholesale prices already seen in the region, there is reason to suspect that prices in the areas supplied by these facilities may continue to rise until the situation is resolved."

Nationwide, prices are rising due to corn prices which have caused ethanol costs to increase about 17 percent in July, according to the Huffington Post.

Gas prices rise four times faster than they fall after the wholesale price changes, according to a 2010 Federal Trade Commission (FTC) study. USA Today says that, according to the study, some retailers sell at a loss when wholesale prices are high and try to make up for it when prices go down.

AAA says prices should begin to decline again after Labor Day.