Barcelona - Ferrari's Sebastian Vettel was fastest in F1 testing, ahead of Mercedes' Nico Rosberg.
Vettel led the first of two days of testing at the Barcelona track, one tenth of a second faster than Rosberg. Jenson Button of McLaren was third, half a second behind Vettel.
Vettel, Rosberg, and Renault rookie test driver Esteban Ocon ran more than 100 laps each. Sauber was the only team not to participate.
Ten drivers participated in the session, which happened only two days after the Spanish Grand Prix was won by Red Bull's Max Verstappen.
Vettel was third on Sunday, behind team mate Kimi Raikkonen. Rosberg and team mate Lewis Hamilton crashed into each other on the first lap.