Ahead of today's opening practice session, the air temperature is 21.4 degrees C, while the track temperature is 33.7 degrees. It is bright and sunny.

There are two reserve drivers on duty today, at Williams Roy Nissany replaces George Russell, while Kimi Raikkonen steps aside for Robert Kubica.

Since last year's race, Turn 10 has been re-profiled, which should see higher lap speeds, but, sadly, no improvement in terms of overtaking.

The lights go green and in no time at all there are 12 cars on track, Perez leading the way on hards.

In terms of track limits, Turns 1, 2, 13 and 15 are under observation.

Oh dear, just 4 minutes in and Mazepin is off and in the gravel at Turn 8, however he is able to get going again. Replay shows the Russian had the rear of the Haas step out as he exited Turn 7.

Hamilton complains that his steering is pulling to the right.

Of the first wave, Hamilton goes quickest (21.014), ahead of Bottas, Norris, Gasly and Alonso, the Spaniard being the only driver on softs, the rest are on hards.

However, Verstappen responds with a 20.405.

"Mazepin will never change," says Leclerc as he is impeded by the Russian.

Ten minutes in and all but Perez, Ricciardo and Tsunoda have posted times.

On those softs, Alonso goes quickest with a 19.950. However, on hards, Hamilton responds with a 19.675.

As most return to the pits, the Mercedes pair are running together, possibly looking to practice a tow or two.

Two drivers who really need a strong performance this weekend are Bottas and Perez, the pair are currently 4th (Bottas) and 15th.

The Mexican is informed that his teammate has incurred front wing damage after running over the exit kerb at Turn 8.

Gasly reports that his car is "behaving quite strange". Despite that the Frenchman is currently sixth.

Vettel and Schumacher switch to the softs, as does Mazepin. Haas reveals that, after feeling uncomfortable in his new seat, the Russian has reverted to his old one.

On the red-banded rubber, Vettel goes quickest in all three sectors, crossing the line at 19.234, 0.716s up on Alonso who was similarly shod.

Hamilton switches to the softs and unsurprisingly he goes quickest in the first two sectors, finally crossing the line at 18.808, 0.426s up on Vettel.

"I lost a piece of the front wing," reports Vettel, "coming out of seven."

Having aborted his first flying lap, Bottas now goes quickest in S1, as Stroll goes third with a 19.883.

Bottas crosses the line at 18.838, 0.030s down on his teammate.

Gasly goes third (19.062), ahead of Vettel, Giovinazzi, Stroll and Verstappen, though the Dutchman has yet to try the softs.

PBs in all three sectors are enough for Norris to go third (18.944).

The softs are clearly good for two hot laps, for while Hamilton improves to 18.627, Bottas goes top with an 18.504.

Ricciardo can only manage 9th, the Australian (19.732), around 0.7s off his teammate's pace.

A 19.669 sees Tsunoda go seventh, the Japanese very much off the boil since that Bahrain debut.

Leclerc has successive lap time deleted for exceeding the limits in Turn 2.

The session is red-flagged when Kubica goes off into the gravel at Turn 10, after carrying too much speed. Sadly, the Pole is unable to extricate himself from the kitty litter.

Tsunoda is told that he needs more speed in all the corners.

The session resumes with 9 minutes remaining, the Bulls yet to try the red-banded tyres.

Both head out on the softs but with 19 drivers on track traffic is certain to be an issue. Interestingly, Leclerc has shunned the softs for the mediums.

Perez goes sixth on the softs (19.349), while teammate Verstappen aborts his lap after coming across a slow Stroll.

Also on mediums, Sainz goes fourth (19.020), with his teammate posting a 19.051 to go fifth moments later.

On his next flying lap, Verstappen posts a PB in S1 and again in S2, finally crossing the line at 18.537 to go second, despite it being a very scruffy lap.

Norris heads out on softs, the left side of his car smothered in flo-vis.

Having posted successive PBs, Perez' next flying lap is ruined when he comes up behind a slow Ricciardo.

The session ends. Bottas is quickest, ahead of Verstappen, Hamilton, Norris, Leclerc, Sainz, Gasly, Vettel, Perez, Stroll and Tsunoda.

Ocon is eleventh, ahead of Giovinazzi, Ricciardo, Alonso, Latifi, Nissany, Schumacher, Kubica and Mazepin.

Check out our Friday gallery from Barcelona, here.