Have you ever wondered: Why are gas prices in Sioux Falls more expensive than in Rapid City recently?

SIOUX FALLS, S.D. - Right now the national average price for a gallon of gas is $2.52. The state of South Dakota's average is a few cents more at $2.56 per gallon. Drivers in Rapid City are paying on average $2.36, which is well below the national average. But in Sioux Falls, they're paying $2.58 per gallon when usually they're paying much less than west river drivers.

Jodie Sixtoes is the general manager at a Sioux Falls gas station. She said at her BP station on Kiwanis Avenue and West Russell Street, it varies how often gas prices change.

"We change our prices from every single day to once a month. It all depends on how many loads you have coming in, how often the loads are changing prices. Your weather plays a factor. Holidays play a factor," Sixtoes said.

But usually Sioux Falls is still cheaper than Rapid City. The head of petroleum analysis at Gas Buddy, Patrick DeHaan, said it's because the market is more competitive than Rapid City.

"There's more suppliers. It's a bigger pipeline coming into Sioux Falls, which helps keep prices lower; whereas, Rapid City is a smaller pipeline, end of the pipeline, less competitors," DeHaan said.

Rapid City gets its oil from refineries in the Rocky Mountains. Sioux Falls is hooked up to the Midwest. He said sometimes the regions have completely different prices because of this.

"What I imagine is happening in the last few months to drive prices much lower in Rapid City is it looks like the disconnect started shortly after Hurricane Harvey," DeHaan said. "And that's probably because the Rockies are more isolated away from the interconnectedness of the rest of the country."

On top of that, more gas stations have opened in Rapid City within the past year, creating more competition.

"New station opens up. What's the best way to let everybody know? By offering a cutthroat price on gas and that can make everybody, every station in the area lower their prices," DeHaan said.

But the effect could be only temporary. Across the country, drivers will start using the summer blend of gasoline in April. That tends to be more expensive, a price that is typically passed onto the consumer.