Ahead of today's opening session, the air temperature is 24 degrees, while the track temperature is 29 degrees. It is bright and sunny, but there is quite a lot of cloud drifting over the Mediterranean.

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

The lights go green and the Force Indias lead Nick Heidfeld as the Monaco GP weekend gets underway. Buemi and Vettel are among the others keen to get to work.

Nine minutes into the session all but Raikkonen have been out, at which point the 2007 World Champion heads down the pitlane. The Finn completes the obligatory installation lap then heads back to his garage.

Heidfeld is the first driver to come out for a second run, his team needing to take a significant step forward. The German completes just one lap before returning to the pits, his place out on track taken by Buemi.

The Swiss driver crosses the line to post the first time of the day (1:25.201), improving to 22.896 next time around. Elsewhere, Timo Glock heads down the pitlane.

Buemi improves with a 21.805, as Glock posts 24.560. Trulli, Massa, Raikkonen and Bourdais are all on track.

Glock improves to 23.321, as Toyota teammate Trulli posts 25.630 to go third.

Massa goes quickest with a 20.665, ahead of Buemi, Glock, Trulli and Bourdais, as Piquet leaves the pits.

As Massa goes quickest in the first two sectors, Glock goes quickest with a 20.548, the Ferrari driver subsequently re-taking the top spot with a 20.162. Raikkonen goes sixth with a 24.304.

Massa posts 19.278 as teammate Raikkonen improves to second with a 19.935. Button goes seventh (21.727) as Nakajima, Webber, Rosberg and Alonso leave the pits.

World Championship leader Button improves to second (19.669) - Massa having improved with an 18.953 - as Kovalainen goes fourth, ahead of Glock, Raikkonen and Piquet.

Massa goes third and Hamilton fourth, the lap times tumble as the grip improves and the drivers gain confidence.

Hamilton goes quickest in the first two sectors, finally crossing the line at 18.376 to take the top spot. All but the BMW drivers have posted times.

Rosberg, currently fifth, goes quickest in the middle sector, finally crossing the line at 18.399 to go second. It's business as usual - at least, Friday business as usual - for Rosberg and Williams.

Hamilton is the first driver to break the 1:17s barrier, the McLaren driver crossing the line at 17.578. The reigning World Champion is pushing very hard, the rear end of his McLaren just a whisker away from the barriers at various points on the track.

At half-time, it's: Hamilton, Webber, Barrichello, Rosberg, Alonso, Massa, Button, Nakajima, Raikkonen and Vettel. That said, the order is constantly changing, such is the frenetic pace here this morning.

Heidfeld complains of brake problems, which he feels make the car "dangerous to drive". He claims that he suffered similar problems in Spain, which is where BMW introduced its upgrade. The German, like his Polish teammate, has yet to post a time.

Kovalainen (6th) takes to the escape road at Ste Devote as he gets it all wrong.

Massa takes second with an 18.105, as Heidfeld goes nineteenth (of nineteen) with a 22.219.

Bad news for Vettel, his engine let's go halfway through the tunnel. He heads back to the pits a trail of blue smoke behind him, but hopefully no oil. The German is currently tenth on the timesheets.

Oil or no oil, Barrichello goes quickest in the middle sector, crossing the line at 17.505 to take the top spot. Next time around the Brazilian consolidates his position with a 17.189 as Massa goes second (17.499).

Webber complains of a "vibration" and ask his crew to check the data. A good call considering his teammate's fate.

Kubica improves to eighteenth, one place behind his BMW teammate, as Trulli remains rooted to the foot of the timesheets, the Toyota driver having completed 17 laps.