Internet sales are transforming the $81 billion North American used-car auction business, according to The Wall Street Journal.

Since the 1930s, giant regional auction yards have

been the primary place for dealers to buy and sell cars previously used for rentals or leases, according to the Journal. Automakers and dealers still send many used vehicles to the auction houses by truck. On auction day, buyers from dealerships around the region inspect the cars and bid for the ones they want. Winning bidders send their purchases back to their dealership on trucks.

The largest U.S. wholesaler -- Manheim Auto Auction, a unit of Cox Enterprises Inc. -- says sales on its Web site have increased 30 percent to

150,000 cars this year, compared with the company's total annual sales of five million cars. Dean H. Eisner, chief executive of Manheim, said he believes that online transactions could grow to as much as 10 percent to 15 percent of the market.

There are still good reasons to bring cars to auction sites, Eisner said: "Part of it is, if you're a rental-car company, you need a place to put your cars when the new fleet comes in."

Many automakers also like physical auctions because those venues provide a benchmark for

prices in the industry, according to the Journal. "We still believe that the traditional auction is the best way to establish a market," said Linda Silverstein, director

of Ford Motor Co.'s remarketing-business operations.