Williams will keep an unchanged line-up of Germany's Nico Rosberg and Japan's Kazuki Nakajima next season, the Formula One team have announced.

The Toyota-powered former world champions said in a statement that 21-year-old German Nico Hulkenberg would also remain as test and reserve driver.

With Formula One's technical regulations changing considerably, Williams said continuity was a key consideration.

Rosberg, 23, was already under contract for 2009 after team founder and co-owner Frank Williams last year rejected what he called an offer of "majestic proportions" from Mercedes-powered McLaren.

However, Toyota protege Nakajima, son of former racer Satoru and currently Japan's only grand prix driver, had been waiting to hear whether he would be retained for a second season.

"Nico Rosberg continues to be one of the most capable drivers in the sport," said Frank Williams in the statement.

"Kazuki is getting stronger all the time and has more to offer and Nico Hulkenberg is developing well."

The announcement came after the British-based team celebrated their second podium finish of the season in Singapore's inaugural night race last weekend.

Rosberg, son of Finland's 1982 world champion Keke, finished a career-best second while Nakajima took a point in eighth place.

Williams, who last won a grand prix in 2004, are currently eighth in the constructors' championship with three races remaining.