BMW and the Williams racing team on January 10 officially unveiled their Formula One car for the coming season while saying an unnamed main sponsor had finally been signed, according to reports from Munich.

The sleek car driven onto the stage bore BMW's colors of white with blue racing stripes and marked the return of the German auto manufacturer to the circuit after a 12-year absence.

But the new livery wasn't emblazoned with the logo of a main sponsor, leaving the Williams team boss to squash the ongoing reports the team faced a 40 million US dollars budget gap.

Frank Williams said the new sponsor would be announced in Barcelona at the end of January.

Williams said BMW-Williams hadn't settled on a second driver behind two-time world champion Michael Schumacher's younger brother, Rolf. The team is still negotiating with last year's driver, Alex Zanardi, while testing two young drivers.

BMW will have its latest engine, the FW 22-B, installed in timefor test runs at Barcelona. But Schumacher, who drove a Super-Tec from Renault last year, already was high on the engine.