The Formula One world champion Jenson Button believes as many as seven teams are serious title contenders for the 2010 season.
He says there are four major ones, his McLaren team, Ferrari, Mercededs and Red Bull but says Sauber, Team India and Williams aren't far behind.
Compatriot and team mate Lewis Hamilton, the 2008 world champion, finished fastest in the final pre-season testing session in Barcelona while seven-times world champion Michael Schumacher of Mercedes came in sixth despite being out of the sport since 2006.
The first race of the season is in Bahrain in a fortnight.
