Back in F1 after two years away, 2007 world champion Kimi Raikkonen dominated the first day of testing at Jerez today.

All but Marussia were in action as preparations for the 2012 season, which begins in Melbourne in just over five weeks, finally got underway.

Though Mercedes and HRT ran their 2011 cars, their nine rivals had their 2012 contenders in action, Ferrari, in particular, making good use of the 'nose bump' that is a feature of this year's car.

Raikkonen posted his best time of 1:19.670 quite early in the session, the Finn completing 75 trouble free laps. Though the Enstone-based outfit was keen to play down the significance of lap times at this early stage, it is an encouraging start, especially for its Finnish driver.

"It was a positive first day of testing and everything went almost to plan," said Raikkonen. "We had no major issues and I got a good feel for the car and the tyres. The tyres were more of a challenge in the afternoon when we ran with a scrubbed set, but overall it was a positive day. The lap times don't matter today. I'm happy with the balance of the car, which feels good, and the fact that we didn't have any major issues. Also, I did more than a race distance today and did not have any physical problems at all, which is good. I'm looking forward to making further progress with the car tomorrow."

"It was a flawless morning with a slightly interrupted afternoon as we changed the second of the KERS batteries which we ran today," said technical director, James Allison. "Overall it was a very promising day in terms of reliability and it gives us a good springboard for the rest of the test. So far Kimi's feedback on the car has been complimentary in terms of the balance, the braking and other features. The steering is slightly heavy for his liking at the moment, but we already have a different steering rack being completed which he will use in Barcelona."

"We enjoyed a strong first day with the E20 in both performance and reliability," added Alan Permane, the team's trackside operations director, "and this is a testament to all the hard work done by everyone at Enstone over the winter. It's always nice to be top of the timesheets, but the main encouraging factor from today is the car's reliability; apart from a small KERS problem this afternoon it was faultless. We ran on the medium compound Pirelli tyre all day and it seemed to hold up pretty well, showing similar degradation to that we saw last year, so I think there'll be exciting racing once more in 2012."

Paul Di Resta was behind the wheel for Force India as the team started systems checks, data collection and set-up work. The Scot was the second busiest driver out there, completing 101 laps on his way to posting the second best time.

"A good start to our winter test programme with 101 laps completed, which allowed us to get through all our objectives and a bit more," said the Scot. "The baseline balance felt pretty good and the car performed consistently over the longer runs, which was useful for collecting the data we need. So I think we can be positive heading into tomorrow and the next three days will be interesting as we have more test items to evaluate. On a personal level it's also nice to spend such a busy day in the car to shake off the rust and assess my fitness level."

"To complete over 100 laps on the first day of testing is the ideal way to begin our week in Jerez," added technical director, Andrew Green. "We made good progress with the job list and managed to complete all the objectives set for the day. We ran on the new 2012-spec hard and medium Pirelli tyre compounds throughout, which will help give us some consistency when analysing the data tonight. As usual, Paul's feedback was excellent and we're starting to get a good idea of the set-up direction we should take for the coming days.

"Jules will be in the car tomorrow morning so the priority is to get him comfortable and up to speed quickly. We will also continue with more of the work we started today and try to get as many miles on the car as possible."

Mercedes ran Nico Rosberg in the morning and teammate Michael Schumacher in the afternoon. Between them the German duo posted 98 laps, Rosberg's best time an encouraging 0.575s quicker than his teammate.

Both drivers completed a set-up programme which focused on learning about the behaviour of the 2012 Pirelli tyres, the highly reliable 2011 car also allowed the team to accumulate valuable mileage on a number of test items for the 2012 season. Schumacher will continue the programme tomorrow, with Rosberg in action again on Thursday.

"We made a very good start to our programme today and completed 56 laps this morning," said Rosberg. "I was driving the 2011 car, so it felt comfortable straightaway. We tested some different things in perfect weather conditions and started learning about the 2012 Pirelli tyres and how they work. I was really happy to be out on track in my Mercedes and I know that, back at the factory, our development of the new car is running according to our plan."