The team said in a statement at the Brazilian Grand Prix that 19-year-old German Sebastian Vettel would be their official test and reserve driver.

"For me to be confirmed as a driver for the team in 2007 proves that in the last five races I have done the job expected of me," said Kubica, 21.

The Pole, his country's first Formula One driver, replaced Canadian former champion Jacques Villeneuve at the Hungarian Grand Prix in August and finished third at Monza last month in only his third Formula One race.

"I feel I can start my 2007 season now," he added.

Heidfeld, 29, had a firm contract for 2007 and was sure to continue with the team while Vettel has impressed in the Friday practice sessions he has done as a third driver.

"This is a tremendous step in the right direction," said the teenager. "I have always dreamed of sitting in the cockpit of such a fast car on a regular basis.