General Motors and PSA Group posted weaker European sales in January than any other major carmaker as they discuss a possible purchase of GM's European car operations by PSA.
A combination between GM and PSA would create a manufacturer with about 16% of the European passenger car market, ahead of French rival Renault and behind Germany's Volkswagen.
New passenger car registrations at PSA, including the Peugeot, Citroen and DS brands in the European Union and the European Free Trade Association rose 6.5% in January.
This compared with 5.3% for GM's Opel and Vauxhall brands, the Association of European Carmakers (ACEA) said.
But the Volkswagen group, nearly a year and a half after its emissions scandal came to light, racked up 10% growth last month, as did Renault, according to Brussels-based ACEA.
Fiat Chrysler Automobiles recorded a 15% rate of expansion while Ford came in at 9.5%.
Overall registrations in the region jumped 10% on extra selling days to 1.204 million vehicles from 1.094 million a year earlier, ACEA said.
The UK's largely foreign-owned car industry has thrived in recent years, but the vote to leave the European Union has cast doubt on future growth by raising the prospect of tariffs which would make UK plants less competitive.
Britain posted the lowest rate of growth among the seven largest EU markets in January at 2.9%, compared with around 10% expansion each in Germany, Italy, France and Spain.
In the high-margin segment, Germany's leading luxury nameplates Mercedes-Benz and BMW posted 16% and 11% growth respectively, faring better than VW's Audi brand at 3.1%, according to ACEA.
