Heidfeld leads practice 3 - Spain

The German leapt from 19th position to first when he switched to the softer tyres for his final run.

David Coulthard took second for Red Bull, ahead of Renault's Fernando Alonso.

Ferrari and McLaren appeared to continue their recent strategy of running heavier fuel loads in this practice session. Felipe Massa and Kimi Raikkonen were only ninth and 13th in the Ferraris, while McLaren teammates Lewis Hamilton and Heikki Kovalainen ended the morning 11th and 15th respectively.

A frenetic opening half-hour saw six drivers swapping first position, and as many as 16 cars covered by just one second.

Raikkonen was the first of the major contenders to complete a flying lap, and immediately went fastest on a 1:22.804, but within two minutes Kovalainen and BMW's Robert Kubica had both usurped the world champion.

Alonso was next to go fastest overall, to the delight of the home fans, and although his 1:22.634 was swiftly beaten by Rubens Barrichello (Honda), the Spaniard improved to a 1:22.271 on his next run to lead the way again.

Coulthard then moved ahead in the final 20 minutes, initially beating Alonso with a 1:22.068 lap and then improving to a 1:21.580 on his next outing - both times achieved on the harder Bridgestones.

The Scot remained on top until most of the field switched to soft tyres with four minutes remaining. He improved his own time to 1:21.465 on the soft compound, but this was not enough to beat Heidfeld and he had to settle for second.

Alonso jumped to third in the closing moments, with Kubica and Toyota's Jarno Trulli completing the top five.

Sebastien Bourdais was a surprise sixth for Toro Rosso, ahead of Alonso's Renault teammate Nelson Piquet and Honda driver Jenson Button.

Behind Massa, Timo Glock took the final top ten spot in the second Toyota.

Mark Webber failed to set a time in the second Red Bull. A suspected throttle problem caused the Australian's car to come to a halt in the pit exit before he could complete a flying lap.

As had been the case in Friday practice, the braking area for the tight Turn 10 was the scene of the session's main incidents, with both Barrichello and Force India's Adrian Sutil spinning down the asphalt run-off there before rejoining without drama.

Pos  Driver       Team                      Time               Laps
 1.  Heidfeld     BMW Sauber           (B)  1:21.269           19
 2.  Coulthard    Red Bull-Renault     (B)  1:21.465  + 0.196  16
 3.  Alonso       Renault              (B)  1:21.599  + 0.330  16
 4.  Kubica       BMW Sauber           (B)  1:21.717  + 0.448  23
 5.  Trulli       Toyota               (B)  1:21.771  + 0.502  21
 6.  Bourdais     Toro Rosso-Ferrari   (B)  1:21.942  + 0.673  19
 7.  Piquet       Renault              (B)  1:21.992  + 0.723  18
 8.  Button       Honda                (B)  1:22.060  + 0.791  17
 9.  Massa        Ferrari              (B)  1:22.075  + 0.806  16
10.  Glock        Toyota               (B)  1:22.081  + 0.812  23
11.  Hamilton     McLaren-Mercedes     (B)  1:22.094  + 0.825  15
12.  Rosberg      Williams-Toyota      (B)  1:22.174  + 0.905  19
13.  Raikkonen    Ferrari              (B)  1:22.176  + 0.907  18
14.  Nakajima     Williams-Toyota      (B)  1:22.189  + 0.920  16
15.  Kovalainen   McLaren-Mercedes     (B)  1:22.220  + 0.951  16
16.  Vettel       Toro Rosso-Ferrari   (B)  1:22.292  + 1.023  20
17.  Barrichello  Honda                (B)  1:22.350  + 1.081  17
18.  Fisichella   Force India-Ferrari  (B)  1:22.466  + 1.197  22
19.  Sutil        Force India-Ferrari  (B)  1:22.689  + 1.420  21
20.  Sato         Super Aguri-Honda    (B)  1:23.726  + 2.457  16
21.  Davidson     Super Aguri-Honda    (B)  1:23.921  + 2.652  15
22.  Webber       Red Bull-Renault     (B)                     2

All timing unofficial