Rubens Barrichello took Williams to the top of the timesheets on the final day of this week's Jerez test, setting the fastest lap of the week with a 1m19.832s.
The Brazilian's best time came on the last of a series of eight-lap runs that he embarked on early in the day, as he got plenty of mileage following Williams's delays earlier in the test.
There was a 1.3-second drop-off immediately after his benchmark 1m19.8s, though his times only faded by 1.2s over the rest of the stint.
Barrichello later produced the longest stint of the test so far in the afternoon, completing 25 laps that started in high 1m26s for 16 laps before slipping away to low 1m29s by the end. The Williams caused one of several red flags by stopping on the back straight with a hydraulic leak during the final hours.
Second-placed Kamui Kobayashi was another to trigger a stoppage when he put his Sauber into the gravel in the morning. His 1m20.601s best was something of a one-off, as his short morning runs tended to be in the 1m22s region. His afternoon was slightly interrupted by a powertrain issue, but still featured some consistent long stints, presumably on the harder Pirellis as his times dropped off by less than a second after 15 laps.
Crowd favourite Fernando Alonso placed the Ferrari third. This time also came during a short morning run before he switched to long, heavier-fuel stints for the afternoon. He did three runs of between 16 and 20 laps, with a pace drop-off of around two seconds from start to finish.
Sebastien Buemi kept Toro Rosso near the front in fourth, as he also followed the pattern of morning sprints followed by an afternoon on heavier fuel.
He was just ahead of Renault reserve Bruno Senna, who was 1.5s off the pace in fifth on his first day in the car. The Brazilian was being given development mileage for experience rather than as an evaluation for Robert Kubica's vacant seat, which seems certain to go to Saturday pacesetter Nick Heidfeld.
Despite losing some time with a water leak, Lotus again set an attention-grabbing time with sixth for Heikki Kovalainen. He did mostly short stints in 1m21s and 1m22s, eventually beating his Saturday best by a tenth.
Nico Rosberg did not repeat team-mate Michael Schumacher's pace for Mercedes and seems to be suffering the brunt of Mercedes' pre-season reliability troubles. He was seventh, having had a long delay in the pits as his car received a precautionary engine change after stopping on track in the morning.
The Red Bull RB7 continued on its path under the radar, with Sebastian Vettel setting just the eighth-fastest time today. That came early this morning and he spent the rest of the day doing long runs, seemingly with a lot of fuel in the car. His longest run was of 19 laps, holding steady in the 1m25s and 26s.
McLaren too showed no signs of chasing laptimes as Jenson Button worked mainly on long stints, lapping in the 1m25s for the vast majority of a 19-lap run this afternoon. Button was unhappy with the car's balance, though, and a mechanical problem then kept him in the pits during the later hours.
Virgin did not do much before Jerome D'Ambrosio stopped on track this morning. The team said it was going to replace an oil sensor but it turned out to be a four-hour delay before the Belgian returned for a short outing late on.
Paul di Resta was at the foot of the times for Force India. The Scot went off at the Dry Sack hairpin with just under half an hour remaining, due to a front suspension problem that pitched him into the gravel.
While his car was being recovered, grey clouds rolled in and a light rain began. By the time the track went green again, those that ventured back out - Buemi, Barrichello, Alonso and Rosberg - did so on intermediate tyres.
Buemi was consistently the quicker of the quartet, mostly in the 1m36s, but the session concluded before any meaningful wet running could be done or crossover data gathered.
Testing resumes for a further four days at Catalunya on Friday.
Pos Driver Car Time Gap Laps
1. Rubens Barrichello Williams-Cosworth 1m19.832s 103
2. Kamui Kobayashi Sauber-Ferrari 1m20.601s + 0.769s 86
3. Fernando Alonso Ferrari 1m21.074s + 1.242s 115
4. Sebastien Buemi Toro Rosso-Ferrari 1m21.213s + 1.381s 90
5. Bruno Senna Renault 1m21.400s + 1.568s 68
6. Heikki Kovalainen Lotus-Renault 1m21.632s + 1.800s 43
7. Nico Rosberg Mercedes 1m22.103s + 2.271s 45
8. Sebastian Vettel Red Bull-Renault 1m22.222s + 2.390s 90
9. Jenson Button McLaren-Mercedes 1m22.278s + 2.446s 70
10. Jerome D'Ambrosio Virgin-Cosworth 1m22.985s + 3.153s 45
11. Paul di Resta Force India-Mercedes 1m23.111s + 3.279s 99
All timing unofficial