Jean-Eric Vergne remained at the top of the timesheets after the second day of the young driver test in Abu Dhabi.
The Frenchman's running was restricted because of a mixture of sensor troubles during the morning and KERS problems in the afternoon. But Vergne's best lap of 1m40.188s from the morning was enough to earn him top spot.
Ferrari driver Jules Bianchi improved during the final hour, setting a best lap just 0.091s behind with half-an-hour of the day remaining, to finish very close to Vergne.
Despite setting a strong time, Bianchi also had a lot of test work to get through, trying out some new components, conducting engine mapping trials and also running Pirelli's 2012 rubber.
McLaren driver Gary Paffett recovered from causing a red flag during the morning session when he lost oil, ending up third overall ahead of Valtteri Bottas in the Williams.
The Finn lost a little time around the lunch break when he suffered a wiring problem, but was soon able to return to the track after a delay at the start of the afternoon.
He was due to head to the airport soon after stepping out of the car to complete a dash to Macau for the Formula 3 Grand Prix, with first practice for that event starting only 14 hours after the chequered flag today.
Esteban Gutierrez made his first appearance for Sauber since last year's rookie test, ending the day sixth overall behind Force India's Johnny Cecotto Jr and Mercedes's Sam Bird, who continued an intensive schedule of car development work.
Cecotto Jr was the the best F1 debutant ahead of Formula Renault 3.5 race-winner Kevin Korjus, eighth overall.
Also running today were Luiz Razia (Lotus), Kevin Ceccon (Toro Rosso) and Jan Charouz (HRT), with Charles Pic continuing in the Virgin and ending up slowest overall after losing time in the morning while the team worked on changing an engine-related system component that required the floor to be removed.
Nathanael Berthon also appeared during the final half-hour, taking over Charouz's car. He will return for a full day of running tomorrow.
Pos Driver Team Time Gap 1. Jean-Eric Vergne Red Bull-Renault 1m40.188s
2. Jules Bianchi Ferrari 1m40.279s + 0.091
3. Gary Paffett McLaren-Mercedes 1m41.756s + 1.568
4. Valtteri Bottas Williams-Cosworth 1m42.367s + 2.179
5. Johnny Cecotto Jr Force India-Mercedes 1m42.873s + 2.685
6. Esteban Gutierrez Sauber-Ferrari 1m43.637s + 3.449
7. Sam Bird Mercedes GP 1m43.734s + 3.546
8. Kevin Korjus Renault 1m43.776s + 3.588
9. Luiz Razia Lotus-Renault 1m43.944s + 3.756
10. Kevin Ceccon Toro Rosso-Ferrari 1m44.808s + 4.620
11. Jan Charouz HRT-Cosworth 1m46.644s + 6.456
12. Charles Pic Virgin-Cosworth 1m46.698s + 6.510
13. Nathanael Berthon HRT-Cosworth 1m48.646s + 8.458
All Timing Unofficial