The average price for gas has dropped recently in the U.S., despite refinery issues in the Midwest.

With the stock markets across the world in turmoil, oil prices are continuing to spiral downward and gasoline prices are also tumbling as the end of the summer driving season.

The average U.S. gas prices are at the lowest levels for this time of year since 2004 — the year before Hurricane Katrina shut down refineries along the Gulf Coast — due to the continuing decline in the cost of crude oil, according to the AAA’s weekly survey.

Gas prices have dropped despite ongoing refinery problems, particularly in the Midwest, and prices are expected to fall this autumn due to declining demand and the switchover to winter-blend gasoline.

The national average price of gas is $2.59 per gallon, which is eight cents less than a week ago and 84 cents less than a year ago. Pump prices are now 21 cents per gallon below the 2015 peak price reached on June 15, AAA reported.

AAA said the weekly price comparisons continue to reflect volatile fluctuations in the balance between regional supply and demand. Just a week after Midwestern drivers were reeling from sharply higher pump prices, motorists in these same states have seen prices plummet week-over-week: Indiana, Ohio and Michigan dropped 19 cents pump prices in Illinois dropped by 13 cents.

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BP’s largest crude distillation unit at its Whiting, Indiana, refinery remains out of commission, due to a malfunction reported on Aug. 8 that triggered dramatically higher prices in the Great Lakes region. Repairs to the unit are reported to be ongoing, and the company has yet to release a date they expect the unit to return to production.

However, BP has purchased additional fuel supply and met all of its contractual requirements to date. Although regional supply is still uncertain due to the outage, prices in the region have moved lower over the past week as speculation has built that supply issues might not be quite so dire as ample fuel is available on the open market.

Motorists in the Pacific Northwest continue to pay the nation’s highest averages, with five of the six states with averages above $3 per gallon located in this region. California, at $3.47 per gallon, leads the market, and is followed by regional neighbors Alaska, at $3.43, and Nevada at $3.18 and Washington, at $3.04, as the nation’s most expensive markets for retail gasoline. Drivers in South Carolina, at $2.11, are paying the lowest average at the pump.

Retail averages are down in 44 states and Washington, D.C. month-over-month.

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The largest discounts in the price of retail gasoline were in California where prices dropped by 36 cents per gallon and New Jersey where prices fell by 25 cents per gallon.

Consumers in 33 states and Washington, D.C. are enjoying monthly savings of a dime or more per gallon at the pump. On the other end of the spectrum, retail averages have moved higher in six states over this same period. Prices are double-digits higher in five Midwestern states compared to one month ago: Indiana where prices have gone up by 30 cents per gallon, Illinois by 26 cents, Michigan by 17 cents and Ohio and Wisconsin by 16 cents per gallon.

Year-over-year discounts in the price of retail gasoline persist, largely due to the price of crude being significantly discounted from this date in 2014. Crude oil prices have continued to sag, due to persisting global oversupply and concerns about the health of the Chinese economy. China is one of the world’s largest and most rapidly growing economies.

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Evidence of slower than projected growth in the Chinese economy is rippling through global markets and has put additional downward pressure on the price of crude, which traded below $40 per barrel.