Ahead of today's opening session, the air temperature is 26 degrees C and the track temperature is 29 degrees. Humidity is 54%. It's bright and sunny, albeit with a lot of cloud, but, according to the forecasters - and our very own Bob Constanduros - there is the very real threat of rain over the next two days particularly during qualifying.

Tyre options are medium (prime) and super-soft (option) however, with the title fight so finely balanced the big question is engines.

Well, going into this weekend almost everybody in on 8, except for Felipe Massa and Nick Heidfeld who are on 9, while Rubens Barrichello and the Renault and Hispania duos are all on 7.

That said, some of these engines have only done low-mileage so the situation is not as bad as it appears, certainly for some drivers. Though one only has to think back two weeks to Sebastian Vettel's demise in Korea to appreciate that anything can - and probably will - happen.

As if the thought of five drivers still (mathematically) battling for the title wasn't enough, last night Mark Webber reignited the team bias row at Red Bull claiming that the Austrian outfit's heart is behind Sebastian Vettel. Ferrari and McLaren would be well advised to take full advantage.

Jerome d'Ambrosio is in Lucas di Grassi's Virgin for this session while Christian Klien is replacing Sakon Yamamoto for the entire weekend.

The lights go green and Buemi leads the way, ahead of d'Ambrosio, Trulli, Klien, Alguersuari and a host of others. Hamilton and Button are among the early risers, as is Alonso.

Buemi, who has a grid penalty following the incident in Korea, is the first driver to post a time (1:27.979), the Swiss driver really needing to produce something special if he is to keep his seat.

Five minutes into the session all twenty-four drivers have been out, however, only Buemi has posted a time.

Ten minutes into the session Webber and Vettel are back on track, other than the Red Bull duo, the only other driver on track is Glock.

Having completed another installation lap the Red Bulls return to the pits as Hamilton heads down the pitlane.

While the majority of drivers remain in their garages or on the pitwall, the McLaren duo take it in turn to come out, not so much to entertain the fans but to continue the Woking outfit's tradition of using these sessions much like a test.

Twenty-five minutes into the session Buemi is back on track, the Swiss still the only driver to have posted a time. On his first flying lap he takes almost 7s off his previous best, crossing the line at 21.025.

As the Toro Rosso driver makes his way back to the pits, Klien and Petrov come out to play.

Petrov posts 20.059 to go quickest, as Alguersuari and d'Ambrosio head down the pitlane. Petrov improves with a 17.098 as Klien posts 21.357 to go third. In the Williams garage Rubens Barrichello climbs into his car.

Petrov continues to raise the benchmark, the Renault driver stopping the clock at 15.574. Klien improves with an 18.680 to go second only to be demoted by Alguersuari who posts 17.871.

Ferrari tweet that they are to change the engine on Alonso's car between today's sessions. However, the urge fans not to be concerned as this is the best way to manage the Spaniard's mileage.

Petrov has raised the benchmark with a 14.370, ahead of Alguersuari, Klien, Hulkenberg, Kobayashi, d'Ambrosio, Senna and Buemi.

As Hulkenberg encounters traffic, thereby ruining his lap, all eyes are on local hero Massa. The Brazilian crosses the line at 15.848 to go sixth as Heidfeld goes second (14.764) ahead of Hulkenberg.

A 14.152 sees Barrichello - another local hero - go quickest as Massa complains of "too much understeer". Elsewhere, Schumacher, currently fifth, goes quickest in the first two sectors finally crossing the line at 13.643.

Barrichello reclaims the top spot with a 13.546 but it is Webber who grabs the attention, the Australian going third (14.113) on his first flying lap.