During both of their fastest laps the Toro Rosso drivers were running with low fuel, as they tested the performance of the car under qualifying conditions. Vettel completed 89 laps, while Bourdais covered 88 over the course of the day. The duo are expected in action again on Sunday.
McLarens Lewis Hamilton finished third quickest, with team mate Heikki Kovalainen clocking the fourth-fastest time. Both Hamilton and Kovalainen focused on tyre work, but the pair also had enough time to practice some race starts in the pit lane. Both will continue behind the wheel on Sunday.
Just over three tenths down on the MP4-23 of Kovalainen was Robert Kubica in BMW Saubers F1.08. Kubica, fifth, was joined by team mate Nick Heidfeld, who eventually finished in ninth. Both concentrated on the mechanical and aerodynamic set-up of the teams 2008 car and evaluated several new parts to optimise the F1.08s balance.
Renault driver Fernando Alonso finished sixth in the times, just ahead of new team mate Nelson Piquet Jr. Despite cold and overcast conditions, Alonso and Piquet covered 115 laps each and will continue to drive on Sunday.
“Today was a positive day and we achieved good mileage with both cars, without any problems,” said Christian Silk, chief test engineer. “I was happy with the performance of both drivers and we learnt a lot about the car performance-wise, which has given us lots of interesting data to work with tomorrow.”
Red Bulls Mark Webber and David Coulthard, meanwhile, finished in eighth and tenth respectively. Webber and Coulthard carried out general set-up work in two RB4s. Williams also fielded two drivers with Nico Rosberg finishing in 11th and Kazuki Nakajima six tenths adrift in 12th.
Completing Saturdays line-up was Hondas Jenson Button, 13th, and Force Indias Vitantonio Liuzzi in 14th. Button took charge of Hondas RA108 completing 56 laps as he evaluated a number of different set-up options to develop the car's balance, while Liuzzi covered 61 laps before a clutch and driveline problem interrupted his running.
Testing continues at Barcelonas Circuit de Catalunya on Sunday.
Unofficial Saturday times from Barcelona:
1. Sebastian Vettel, Toro Rosso, 1:21.679
2. Sebastien Bourdais, Toro Rosso, 1:21.782
3. Lewis Hamilton, McLaren, 1:22.135
4. Heikki Kovalainen, McLaren, 1:22.511
5. Robert Kubica, BMW Sauber, 1:22.833
6. Fernando Alonso, Renault, 1:22.938
7. Nelson Piquet Jr, Renault, 1:23.002
8. Mark Webber, Red Bull, 1:23.020
9. Nick Heidfeld, BMW Sauber, 1:23.014
10. David Coulthard, Red Bull, 1:23.322
11. Nico Rosberg, Williams, 1:23.347
12. Kazuki Nakajima, Williams, 1:23.948
13. Jenson Button, Honda, 1:23.959
14. Vitantonio Liuzzi, Force India, 1:23.263
