The line-up for the 2006 Formula One season has been completed after Red Bull Racing and new boys Scuderia Toro Rosso confirmed their drivers.
Klien scored nine points for Red Bull last season
Red Bull named Christian Klien as their second driver while Scuderia appointed Vitantonio Liuzzi and Scott Speed.
Klien took over as Red Bull's second driver to David Coulthard this year after impressing in 15 races.
Italian Liuzzi and American Speed form a young line-up for Scuderia and will have Neel Jani, 21, as their back-up.
Speed, who raced this year in GP2, will be the first American to race in Formula One for 13 years.
The last was Michael Andretti, son of 1978 champion Mario, who had an unhappy 13-race stint at McLaren in 1993.
Liuzzi started four times for Red Bull Racing this year and scored a point on his debut at Imola in April.