@SteveS: They've had a year to look at their three rivals, learn lessons and apply that to this year. However they are bound to have teething problems early on - I've always thought it was going a matter of how much not if they had some early issues in Jerez.
Bottas returns to the pits having racked up 19 laps. Rosberg is still pounding the laps out....
Rosberg has just completed 100 laps.
He's also eight tenths quicker than his nearest rival, Bottas. Quite a statement early on from Mercedes.
Sainz joins the fray in his Toro Rosso. Rosberg showing no signs of letting up.
So what do we all make of Vettel's new helmet?
@ehdbjs: It's less problem for a team like McLaren. The team is hardly struggling for cash. It would be devastating for a team like Force India. What it does show is how difficult it is for even a top F1 team to attract sponsorship at the moment.
It's quite noticeable how much fewer sponsors are on the cars than a few years ago. Compare Alonso's McLaren overalls in 2007 to this year.
@ehdbjs: Yep, he kept the number 44.
@AnysignofSauber?: He's in the garage currently.
Finally, Rosberg returns to the pits as Vettel heads out for another run. He's only got 17 laps to his name at the moment.
@bhs46: Bottas, before Massa takes over on Tuesday and Wednesday.
Hello there. Sebastian Vettel beats Rosberg's benchmark, crossing with a 1:22.958.
Some good news for Vettel and Ferrari. It looks like he's coming to the end of a low fuel run as the laps tick down on his pit board, but it's a good sign.
And as I thought, Vettel returns to the pits with his name top of the timing screens.
@Noski: Ricciardo's last run ended with smoke pouring out of his RB11 and we haven't seen him since.
Very impressive turnout for testing.
@Charlton: It doesn't look like we're going to see Lotus today. They are en route to the circuit but had not arrived this morning - a tweet from the team earlier confirmed they should arrive later today.