Kobayashi leads the way at Barcelona on fourth and final morning of F1 testing

The Sauber driver switched to Pirelli's soft compound in the final hour of the morning and was able to get down to a 1m22.312s - thousandths of a second faster than Pastor Maldonado's Thursday benchmark.

Maldonado was also his nearest challenger in this session, getting to within a quarter of a second of the C31 after switching to super softs in the closing stages. The Venezuelan had spent the early morning in race simulation, and racked up more than 80 laps before the lunch break.

He could not deprive Kobayashi of the top spot however, meaning eight different drivers have topped the opening eight mornings of testing.

Jenson Button ended the morning third fastest in the McLaren, having set his best time relatively early on and on hard rubber.

Force India's Paul di Resta was little more than one tenth of a second down the road in fourth, although the Briton's morning was interrupted when he went off into the gravel at Campsa, bringing out about the only red flag of the morning. He was able to return in the final ten minutes.

Felipe Massa finished fifth fastest for Ferrari, which bolted on super softs in the final five minutes but opted to run only installation laps.

Mark Webber put the Red Bull RB8 sixth, just 0.018s ahead of Jean-Eric Vergne in the Toro Rosso.

Webber opted mainly to run on mediums, although he did switch to softs for the final 30 minutes. Vergne meanwhile achieved his time on super softs.

Nico Rosberg finished 1.7s down on Kobayashi in eighth, the German completing 92 laps - the most of any driver - in the W03.

Heikki Kovalainen managed just 16 laps for Caterham before an electrical problem forced the team to do an engine change, and cut his morning short.

Marussia fared even worse, Charles Pic not managing a single run due to suspension troubles.

Morning times:

Pos  Driver         Team            Time                Laps
 1.  Kobayashi      Sauber          1m22.312s           63
 2.  Maldonado      Williams        1m22.561s  +0.249   86
 3.  Button         McLaren         1m23.200s  +0.888   50
 4.  Di Resta       Force India     1m23.304s  +0.992   45
 5.  Massa          Ferrari         1m23.563s  +1.251   56
 6.  Webber         Red Bull        1m23.774s  +1.462   40
 7.  Vergne         Toro Rosso      1m23.792s  +1.480   45
 8.  Rosberg        Mercedes        1m24.092s  +1.780   92
 9.  Kovalainen     Caterham        1m27.047s  +4.735   16