Mercedes appears poised to make a good start in the Formula One season after Nico Rosberg clocked the best lap time in testing in Sunday's final session, bettering teammate Lewis Hamilton's pace-setting effort from the previous day.

Rosberg unleashed a flying lap around Catalunya Circuit of 1 minute, 20.130 seconds, more than four-tenths quicker than Hamilton's best time on Saturday.

Ferrari can also be confident it has increased its speed from last season, with Fernando Alonso hitting the second-best time of all 12 days of testing in Spain, just 0.364 seconds behind Rosberg.

The season opens at the Australian Grand Prix on March 17.

Rosberg set his blistering mark on soft tires designed for speed during the morning session under a second straight day of clear skies after rain had dampened the track earlier in the week.

The German driver, who won his first race last season, then made longer runs after the lunch break to end the day with a session-high 131 laps completed.

"I'm pleased with our preseason testing program," Rosberg said. "We have achieved a lot of mileage and I can feel that the balance of the car is good."

Rosberg, however, was careful not to draw too many conclusions from testing, which has been held during colder than normal temperatures, affecting tire performance by leading to greater degradation.

"I have the general feeling that we are in a better position than in the second half of last year. But this is testing, not racing, of course," he said. "The conditions in the first race will be completely different to here as it will be much hotter in Melbourne and Sepang, so we need to wait and see."

Mercedes, which came fifth in the constructors' standings last season, was hampered by mechanical problems throughout the year. It has since replaced retired great Michael Schumacher with Hamilton, a former world champion himself who joined from McLaren.

"Lewis (Hamilton) has settled into the team extremely well," said team principal Ross Brawn. "I am pleased with the progress that the team has made over the last month and the steps forward that have been made with the car. We're realistic about our performance here and our position once we get to Melbourne, and we look forward to the challenge of a new season ahead."

Jenson Button of McLaren had the third fastest time, followed by new Sauber driver Nico Hulkenberg and Lotus' Kimi Raikkonen, who missed yesterday's running because of a stomach illness.

World champion Sebastian Vettel had the eighth quickest lap, in between Williams pair Pastor Maldonado and Valtteri Bottas.

Red Bull said it spent the day focusing on race preparations instead of going for good individual lap times, leaving many to believe that the three-time defending champions have yet to show their cars' full potential.

"Over the past couple of days we maybe didn't tick all the boxes that we wanted to, but we have a bit of time left to prepare before the season starts," said Vettel. "The target is there to improve and we will do that. I'm looking forward to Melbourne."

Drivers got the most out of the final test day, with seven out of the 13 who took the track getting in more than 100 laps.