DENISON, Texas (KTEN) — While gas prices have started dropping from record highs across the nation, the cost for a gallon of regular remains significantly higher in southern Oklahoma than just across the Red River.

AAA's latest gas price survey shows the average price for a gallon of regular remains over $4.20 in Love and Marshall counties in Oklahoma. It's lower, at $4.01, in Bryan County.

But the average in Grayson County, Texas, is $3.74, and the price of petrol is also dropped below $4 in neighboring Cooke County.

What's behind the difference? The two states are in different supply zones.

"All of our oil comes from the Gulf Coast and is delivered to Dallas, and then we pick it up from Dallas and bring it to the Texoma area," explained  Douglass Distributing CEO Brad Douglass.. "In Oklahoma, all that motor oil is refined in Ardmore and Wynnewood and actually goes north up into Chicago."

Different supply zones create two different prices when fueling at the pump. More effective refineries along the Gulf mean lower prices for Texas motorists.

"We got a great supply of Texas crude oil," Douglass said. "We have all the refineries on the Gulf Coast, and with that there is just a lot of competition, which really produces very cost effective motor fuel."

You are still paying about $2 more for a gallon of gas than you were just one year ago.