Ahead of today's sole free practice session, the air temperature is 24 degrees C, while the track temperature is 34 degrees. It is bright and sunny.

With no F1 action yesterday (Friday) many of the drivers will be starting from scratch in terms of set-up this morning, track conditions having changed so much since Thursday.

Robert Kubica, who's engine detonated right at the start of the second session, is one driver who will be keen to make up for lost time this morning, while the Toyota duo need to make up ground after a poor showing on Thursday.

Problems at Red Bull also, where Sebastian Vettel suffered an engine failure in the first session, and Mark Webber missed much of the second session as his team sought to find the cause of a worrying vibration.

Only Ferrari and McLaren are using KERS this weekend, while the tyre options are soft and super-soft.

A last minute decision to change the engine in Felipe's Massa means that the Brazilian will miss the first part of today's session. The Ferrari driver doesn't incur a penalty because under the 2009 regulations drivers are allowed 8 engines in total over the course of the season.

The lights go green, and within seconds there are 15 cars on track. Having completed the traditional installation lap they return to the pits.

Jenson Button is warned that Charlie Whiting has sent an e-mail to all the teams advising that drivers are using "too much kerb" at the Chicane and Swimming Pool. Those that fail to keep one wheel on the track can expect to hear from the stewards the Brawn driver is warned.

Seven minutes into the session, all but Massa have been out.

Fisichella is the first driver to come out for a second run, followed by Glock, Trulli and Massa.

The Force India driver posts the first time of the day 1:22.045, but this is quickly eclipsed by Glock (20.242) and Trulli (20.997).

Fisichella improves with a 19.913, but again, Glock goes quicker, crossing the line at 18.626. Elsewhere, Kubica leaves the pits.

As more and more cars pour on to the track, Trulli raises the benchmark with a 17.995.

As the Toyota duo return to the pits, Piquet goes fourth ahead of Kovalainen, Kubica, Webber and Alonso. Almost all are running on old soft tyres.

Having gone quickest in the first two sectors, Hamilton goes quickest overall with a 17.478, as Alonso takes second (17.893).

No sooner has Kovalainen gone third, Rosberg, Alonso and teammate Hamilton all go quicker, the 2008 champion posting 16.791.

As Nakajima goes second (17.233), Raikkonen, on his second flying lap, goes sixteenth with a 18.632. Elsewhere, Kubica gets in the way of Hamilton at the Chicane, causing the Englishman, much to his obvious frustration, to cut the corner.

Rosberg goes second, ahead of Alonso, Webber, Vettel and Nakajima, as Buemi cuts the corner at the Chicane after getting in the way of a Brawn.

A 16.498 sees Raikkonen go second, but he is almost instantly demoted by Rosberg who improves to 16.150. Hamilton consolidates his place at the top of the timesheets with a 15.622.

Raikkonen re-takes second with a 15.986 as teammate Massa posts 16.673 to go fourth.

At half-time, it's: Hamilton, Raikkonen, Rosberg, Barrichello, Massa, Fisichella, Alonso, Webber, Button and Piquet. The Toyotas are fourteenth and eighteenth, while the BMWs are nineteenth and twentieth.

As Fisichella spins at the Chicane, doing well to keep it out of the barriers, Barrichello goes second with a 15.832.

With twenty-one minutes remaining, Hamilton is the first driver to go out on super-softs. The World Champion immediately goes quickest in the first sector, eventually crossing the line at 15.546. An improvement but not by much as expected. Then again, we saw on Thursday that drivers were struggling to get heat into their tyres.