Williams-Toyota have retained Nico Rosberg and Kazuki Nakajima for the 2009 Formula One World Championship season.

Nico Hulkenberg, who is currently leading the Formula 3 Euroseries, will continue as the team's official test driver.

Rosberg and Nakajima are currently lying 12th and 15th respectively in the drivers' overall standings for 2008 and the team is in eighth place. Frank Williams, the Williams Team Principal, said: "I am delighted we are able to maintain continuity with our drivers going into 2009.

"Nico Rosberg continues to be one of the most capable drivers in the sport. Kazuki is getting stronger all the time and has more to offer and Nico Hulkenberg is developing well."

Germany's Rosberg, 23, the son of former F1 world champion Keke Rosberg, has made steady progress since his F1 debut at the 2006 Bahrain Grand Prix, and finished second at the Singapore Grand Prix on Sunday..

Japanese driver Nakajima, 23, is also following in the footsteps of his father, Satoru Nakajima, and made his debut when he replaced the retired Alexander Wurz in last season's final race.

"Kazuki Nakajima has built on his consistency to improve steadily throughout the season. It is the team's expectation that Kazuki will be able to build his natural pace on this firm foundation next season," a Williams statement said.