Ahead of today's qualifying session, the air temperature is 16 degrees C, while the track temperature is 23 degrees. It remains unseasonably cool.

Ominously, Sebastian Vettel has been quickest in all three practice sessions. However, while the McLaren have been in close proximity there is an overwhelming feeling that the German and his team have more in reserve. That said, the Austrian outfit's KERS issue continues with Mark Webber losing vital track time this morning and failing to post a timed lap on soft rubber. Worryingly, his crew has been working furiously on his car since the end of this morning's session and with three minutes to go before the start of Q1 are still working on it.

While there is no doubting Lewis Hamilton's pace in the McLaren, there is concern that the Englishman is being too hard on his tyres, only able to get one hot lap out of his soft while rivals are able to get two or three.

Ferrari is looking a little better today, as is Mercedes, while Renault has seemed a little 'off colour'. Despite various problems, Force India is looking stronger this weekend, while Sauber hopes to benefit from its ability to go easy on its tyres. Williams continues to struggle.

Speaking ahead of the session, Christian Horner confirms that there remains a question mark as to the KERS on Webber's car however, there are no such issues for Vettel.

Perez is first out, followed by di Resta, who is celebrating his 25th birthday today. The Mexican crosses the line at 1:38.295 to get the session underway, with the Scot posting 38.921 moments later.

Heidfeld can only manage 38.501 to go second, however a 38.136 sees di Resta re-take the place. Five minutes into the phase, all but Kobayashi are on track.

Button goes quickest with a 36.778, Hamilton losing time in traffic and therefore only able to manage eighth (39.434). From out of nowhere, Alguersuari produces a 36.156 - aided by his soft Pirellis - to go quickest.

Massa goes third (37.500) but is demoted when Hamilton crosses the line at 36.091 to take the top spot. Vettel's first flying lap sees the German go third with a 36.744 while Buemi makes it a Toro Rosso 2-3 with a 36.355.

Vettel nails the top spot with a 35.891 as Button improves with a 35.924, Rosberg fifth and Webber seventh, the Australian crossing the line at 36.599.

As Vettel looks set to improve, so too does Hamilton, has the Englishman finally learned how to manage those Pirellis? Sure enough, Vettel posts a 35.694 while Hamilton stops the clock at 36.091.

Other than Kobayashi, who has yet to make an appearance, all the usual suspects - Lotus, Virgin and Hispania - are in the danger zone. The Williams, Renaults and di Resta are hovering.

On his first flying lap, Kobayashi goes fifth (36.147), as Heidfeld goes quickest in S1. The German posts a PB in S2 as Perez goes third overall with a 36.046. Moments later, Heidfeld takes second with a 35.910 despite getting it all wrong at Turn 14 and missing the apex.

Di Resta digs deep to produce a 35.702 which sees him go second. Petrov drops into the danger zone with 2:43 on the clock. Both Ferraris on track, both on softs. A sign of desperation from the Maranello outfit?