Mark Webber was fastest today as the last Formula One testing session before the start of the new season got under way.
The Red Bull driver set a best lap time of 1 minute, 21.487 seconds around the Circuit de Catalunya - nearly a second faster than Nico Hulkenberg of Williams.
Nico Rosberg of Mercedes GP, Sauber's Pedro De la Rosa and Jenson Button of McLaren were the only other drivers within two seconds of the Australian driver.
Tonio Liuzzi of Force India was sixth while Fernando Alonso of Ferrari was seventh as the Spaniard was hampered by a mechanical problem.
Webber also had a problem that required his car's removal from the track, with Red Bull mechanics cloaking the vehicle to protect it from prying eyes before it was returned to the garages.
Red Bull is among the leading teams expected to fight for the championship, a group which includes McLaren, Mercedes and current favorite — based on testing form — Ferrari.
But Mercedes motorsport vice-president Norbert Haug said teams will have a better idea of who the front-runners will be by Sunday when testing wraps.
"It's just impossible to judge — it's guesswork," Haug said. "This time is not the benchmark. It's early days, and I would not say that any team has made any serious qualifying efforts so far."
The opening race of the season is the Bahrain Grand Prix on March 14.
Virgin Racing's problematic start continued as rookie driver Lucas di Grassi ran into the tire wall near the close of the morning session to end the team's running on Wednesday. The British team had to fly replacement parts in overnight to fix the damage to the rear of the car.
"Next time I will go even faster, always pushing more and more," Di Grassi wrote on his Twitter page.
Lotus continued its testing program, with Malaysian driver Fairuz Fauzy coming last among the 11 cars — more than six seconds off the pace set by Red Bull.
Fellow rookie teams Campos Meta and USF1 are not in Barcelona, with the latter reportedly on the verge of folding.
The American team is hoping to find sponsorship and funds as it lobbies governing body FIA to allow it to miss the first couple of races since it will not be ready in time.
Campos expects to be ready to race at Bahrain.