Under the deal, BCA's 25,000 account cardholders will be able to advertise their just-bought vehicles for seven days free of charge on the Autotrader.co.uk site.
They can also download the vehicle's details from the BCA database automatically onto the Autotrader.co.uk site.
The service, which is being launched in the spring, will be backed by a marketing campaign in the motoring press and promotions on www.bca-group.com and www.autotrader.co.uk.
Tim Naylor, public relations manager of BCA explained why the new service would be important to dealers who bought many of the one million cars it auctioned each year.
"It gives them the opportunity to turn the car they've just bought back into cash as soon as possible," he said.
He added that the deal was exclusive and that BCA was not looking to tie up similar deals with rival used-car sites.