The average price of gasoline in the United States dipped over the past two weeks thanks to large falls in Midwestern states, coupled with cheaper crude oil, and prices should remain stable or even lower in the weeks ahead, a survey issued on Sunday showed.

Gasoline cost $3.5969 a gallon on average, according to the Lundberg Survey of about 2,500 retail stations taken on June 21. That is 4.16 cents a gallon cheaper than the last survey on June 7, but still 11.89 cents more than a year ago.

That price masked a dollar difference in the price of gasoline in various states. The cheapest gallon could be found in Tucson, Arizona at $3.24, whereas consumers in Chicago had to suffer prices of $4.23.

"Chicago is the still the highest in our panel but it is down just over 25 cents and that is because refinery issues got resolved. The opposite happened in the West - we had fresh glitches," said Trilby Lundberg, author of the widely followed survey.

Prices in the Midwest were driven up earlier this month by outages at large refineries, some unexpected, others planned but lasting longer than at first thought. This included Exxon Mobil Corp's 238,600 barrel per day refinery in Illinois.

These refineries have since resolved their issues but news that Exxon would partially shut down another refinery, this time the 149,500 bpd Torrance, California, plant caused prices to spike in the West.

A lower crude oil price helped pull down the national average although some retailers were quicker than others to pass on the subsequent lower cost of wholesale gasoline, Lundberg said.

"If crude oil prices do not jump or shrink dramatically in the near term, we may see pump prices rather steady, or decline a bit if retailers receiving wholesale price cuts can pass some of that through to motorists," she said.

She said the price of crude oil is being pulled downwards by concerns of an economic slowdown in China as well as signs that the U.S. Federal Reserve will buy less bonds. On the upside are geopolitical risks, especially the continued civil war in Syria.