America's biggest carmaker General Motors has roared away from the competition and posted it best monthly sales in nearly twenty years.

The auto giant's innovative discount promotion, offering consumers vehicles at the same low price a GM employee would pay, led to a soaring 47% rise in sales in June and a market share of 32.8% for the month.

The company launched the offer in an attempt to clear 1.2 million unsold 2005 vehicles before 2006 models arrive this fall - and to win over customers from other brands. It is due to end today (July 5), but may now be extended.

In that event, rivals Ford Motor Company, the US number two, and DaimlerChrysler have signalled they will match GM's offering.

GM's monthly sales totalled 558,092 vehicles, with truck sales at a record 382,601 despite high gasoline prices. About 150,000 of those sales were to new GM customers, with truck sales driving much of that conquest, says Paul Ballew, executive director for market and industry analysis.

June was also a good month for many other car manufacturers in the US. Japanese giants Toyota and Nissan and Honda reported sales up 14%, 19% and 8.9%. respectively. DaimlerChrysler saw sales increase 5.1%.

Ford's sales rose just 0.7%, and the automaker's European luxury brands had mixed results, as Land Rover improved 15%, but Jaguar slid 32% and Volvo dropped 5.7%.

German-headquartered Volkswagen's US sales fell 11%, while compatriot BMW's slipped 3.3%, despite a 17% gain in sales for its redesigned 3-series sedan.

Data sourced from Wall Street Journal Online; additional content by WARC staff