Renault, Nissan and their prospective partner, General Motors, all saw their sales in Europe fall in the first half.
For Renault and Nissan, the rate of decline accelerated in June.
Nissan's sales were down 17.3 percent last month compared with June 2005 and 14.9 percent in the first half, to 172,918 units. The Renault group's sales fell 12.5 percent in June and 9.4 percent in the first half, to 757,729 units.
"As expected, a dearth of new models is hitting Renault sales this year," says Michel Freyssenet, a professor of economics at the University of Evry, near Paris.
"One must hope Renault management won't be so distracted by the GM project that they will neglect to fix the company's product problem."
The three companies have launched a 90-day evaluation of a proposal for Renault and Nissan to buy minority stakes in GM.
Sales of Nissan's Micra small car, Primera and Almera sedans and X-Trail SUV are declining. But with help from the Note minivan launched in February, a Nissan spokesman said the company expects sales to pick up in the second half.
GM's sales fell 8.3 percent in June and 2.4 percent in the first half, to 870,950 units.
A 24.4 percent rise in Saab sales, to 50,264 units in the first half, failed to offset a 4.2 percent fall in Opel/Vauxhall sales, to 728,968 units.
GM's former partner Fiat group is faring best of all in Europe.
The group's Fiat division sales rose 26.1 percent in the first half, to 494,267, and Alfa Romeo was up 10.6 percent, to 80,718.
Overall, first-half sales in Europe were up 1.3 percent, to 8.32 million units. That's 103,754 units higher than in the first half of 2005.
Sixteen countries saw an increase in sales in the first half of the year -- including Germany, Europe's largest market, and Italy. Europe's other large markets -- the United Kingdom, France and Spain -- were down.
You may e-mail Jesse Snyder at [email protected]