At $3.78 per gallon, the national average is the highest for this time of year and 37 cents more expensive than a year ago.
The China news overshadowed signs of improvement in U.S. service companies, which employ nearly 90 percent of the country's workforce. The Institute for Supply Management says its index rose in September at the fastest pace since March.
The U.S. government said crude inventories fell slightly last week but remain 8.4 percent above year-ago levels. Gasoline supplies also rose.
There will be further big price swings in oil this month as the market reacts to each piece of major economic news, says Jim Ritterbusch, of Ritterbusch & Associates. In a daily newsletter, he said oil could jump over the next two days on any positive surprises from the European Central Bank's policy meeting Thursday or the latest U.S. unemployment report on Friday.
In other energy futures trading: