Ahead of today's opening free practice session, the air temperature is 26 degrees C, while the track temperature is 30 degrees. It is bright but fairly muggy, humidity being 59%.

Luiz Razia replaces Jarno Trulli at Lotus for this session, while Hulkenberg replaces Sutil at Force India and Ricciardo replaces Alguersuari at Toro Rosso.

Di Resta is at the end of the pitlane when the lights go green, but as he waits to perform a practice start Kobayashi, D'Ambrosio, Liuzzi and Buemi sweep by. Ricciardo and Karthikeyan are also early risers.

Petrov and Perez are both running new chassis, having damaged their Malaysia cars in separate incidents.

For the third successive weekend, the tyre options are hard (prime) and soft (option). However, all the teams will have an extra set of hard tyres for this session.

Five minutes into the session all but Vettel, Petrov and Kovalainen have been out. While most drivers have completed the obligatory installation lap, Button stays out for a second lap as does Hamilton.

Most of the front running teams are running updates of one sort or another, Ferrari trying a new front wing and brake ducts.

Fifteen minutes into the session, Kobayashi, Barrichello and the Hispania duo are back on track. Karthikeyan is the first to post a time, crossing the line at 1:51.516.

Kobayashi raises the benchmark with a 45.609 as Karthikeyan improves to 48.042 ahead of Liuzzi and Barrichello, the Brazilian crossing the line at 2:04.278.

Both McLarens are on track, Hamilton posting 42.306 having gone quickest in the first and final sectors, while Button goes second with a 43.442. Webber and the Ferraris also on track.

On his second flying lap Hamilton fails to improve while his McLaren teammate posts 41.835 to go quickest. However, third time around Hamilton crosses the line at 41.092 having gone quickest in all three sectors. Webber goes third with a 42.677.

A 42.374 sees Massa go third however, moments later Webber takes the top spot with a 40.692. Maldonado pops up in fifth with a 44.692.

As Ricciardo goes sixth, the Australian putting increasing pressure on Buemi and Alguersuari, fellow Australian Webber goes quickest in all three sectors, consolidating his top spot with a 40.055.

Vettel's first flying lap sees the championship leader go eighth (44.838) as Webber is instructed not to use KERS on his next timed lap. The Australian responds by going quickest in the first sector.

As Vettel runs wide in Turn 6, Hulkenberg posts 42.136 to go sixth. Buemi is seventh, ahead of Ricciardo, di Resta and Kobayashi.

A 40.922 sees Vettel go third, the German immediately posting a PB in the first sector of his next lap despite losing time behind Razia. Replay shows some damage to the front wing on Razia's car, Trulli, watching from the garage, looks mightily unimpressed.

Vettel makes it a Red Bull 1-2, posting a 40.193 to slot in behind his teammate. Next time around however, he goes quickest in the first two sectors and again in the third, crossing the line at 39.540.

At half-time, it's: Vettel, Webber, Hamilton, Massa, Perez, Hulkenberg, Buemi, Button, di Resta and Ricciardo. Still no times from Alonso, Glock or the Renault duo.

Hamilton enjoys a little excursion as the Mercedes duo continue in fourteenth and fifteenth positions. Unsure whether this is poor pace or the German team is simply using this session as a test session pure and simple.

Hamilton's McLaren looking very 'skittish' as Schumacher complains that after nine laps he's beginning to lose the rears. Hamilton, third quickest at this point, is 1.305s off Vettel's pace.

Several teams have been running the flow-viz paint however, Ferrari must take some sort of prize the front wing on Alonso's car covered in the greenish-yellow day-glo paint.