Jenson Button and Nico Rosberg set the fastest laps in each practice session for the Spanish Grand Prix as most teams tested out their updated cars.
Williams' Rosberg went quickest with one minute 21.588 seconds in the second session as Brawn's championship leader Button clocked 1.21.799 in the first.
Times were tight between all drivers as they ran with upgrades they hope will give long-term boosts in performance.
World champion Lewis Hamilton felt his McLaren modifications did not work.
Now into the fifth Grand Prix of the season, Rosberg has topped eight of 14 practice sessions so far - but lies 11th in the championship having only amassed 3.5 points.
BMW Sauber's Robert Kubica and Nick Heidfeld came third and fourth fastest in the first session, which could give the German team a confidence boost - if nothing else - after their disaster in Bahrain where their drivers were the last to finish the race.