DETROIT – Drivers snapped up new models and rental-car companies and governments expanded their fleets in May, leading to big U.S. sales gains for most automakers. The exception was Toyota, whose tepid results showed that the company’s discounts are losing their luster.

The industry’s overall jump in sales shows that automakers are benefiting from a fragile but improving economy. Credit is thawing for car loans and gas prices are stable. Consumers even shrugged off an 8 percent decline in the stock market last month. Ford Motor Co. will boost production through the fall, a sign that it thinks shoppers will keep buying.

Detroit automakers Ford, General Motors Co. and Chrysler Group LLC saw double-digit sales gains over the same month last year, when GM was headed into bankruptcy protection and Chrysler was already there.

Several Japanese, South Korean and European car makers also saw increases of 20 percent or more. If the trend holds for most automakers, May would be the seventh straight month of year-over-year sales increases for the industry.

But consumers backed away from Toyota Motor Co., whose sales rose just 7 percent over last May, even though the company said Memorial Day was its best-selling weekend of the year.

Toyota has been using big incentives since March to drum up sales after it recalled millions of cars and trucks for safety problems.

May’s results indicated those deals may be losing their effectiveness. Only the Lexus luxury brand, which began offering unprecedented deals in May, matched the performance of rivals, with sales up 31 percent. The deals included a six-month waiver on payments.

One key factor for automakers was the long Memorial Day weekend — a key selling period that can account for half of all sales for the month.

Paul Taylor, chief economist with the National Automobile Dealers Association, said good weather and a weak Memorial Day last year — which came just a day before GM filed for bankruptcy protection — helped make sales comparatively stronger during last weekend’s holiday.

Ford’s sales rose 22 percent, boosted by strong demand for the F-Series pickup and new Ford Mustang. Sales to rental, government and commercial fleets rose 32 percent.

But sales fell at Ford’s Lincoln, Volvo and Mercury brands, with Mercury down 11 percent. The company is expected to announce later Wednesday that it’s phasing out the mid-range brand. Ford brand sales climbed 28 percent.