Dealers say the promotion has stirred up business in GM showrooms, which may force rival automakers to come up with their own deals, the St. Louis Post-Dispatch said Sunday.
"If consumers get into the market and start thinking about buying a car, they'll look at all their options," said Lou Fusz Jr., head of Lou Fusz Automotive Network, the St. Louis area's largest dealership group.
Tom Libby, Senior Director of Industry Analysis at J.D. Power, said GM's gains in early June should continue for the rest of the month.
"The GM incentive is very, very effective," Libby told the newspaper. "Every (rival automaker)we looked at lost market share."
Libby said Ford Motor Co. and Chrysler Group of DaimlerChrysler AG are paying attention.
Chrysler's new advertisements highlight its price competitiveness, while Ford is providing cash to employees who pass out employee discounts to friends and family members, he said.