Sebastian Vettel turned to Pirelli's new ultra-soft compound to again the set the fastest time on second day of pre-season Formula 1 testing before the lunchbreak.
Vettel finished the opening day at Barcelona's Circuit de Catalunya quickest on the medium compound with a time posted in the morning session in his Ferrari.
For his second day at the wheel of the SF16-H, Vettel continued to set the pace, initially on the mediums, then the super-softs, prior to a blast on the ultra-softs primarily designed for street circuits.
Red Bull's Daniel Ricciardo was the first to try out the purple-banded rubber late in the session, deposing Vettel with a lap of 1m23.525s.
But Vettel swiftly returned to the top of the timesheets by shaving seven tenths of a second off Ricciardo's time with a lap of 1m22.810s.
Mercedes, meanwhile, continued to focus on mileage, with Nico Rosberg clocking 81 laps over the first four hours of the day after Lewis Hamilton managed 156 throughout Monday.
Running on the medium compound, Rosberg finished third, two seconds off the pace of Vettel.
Force India's Sergio Perez was fourth - also on the mediums - with a 1m25.692, getting his first taste of the VJM09 after reserve Alfonso Celis Jr gave the car its debut on Monday.
In last year's Sauber, with the Swiss team not due to give its new car an airing until the first day of the second test next week, Marcus Ericsson was almost three seconds down in fifth on the soft tyre.
Valtteri Bottas finished marginally behind Ericsson in his Williams, but with a lap on the medium, with Manor's Pascal Wehrlein and Jolyon Palmer for Renault in seventh and eighth, and both using soft rubber.
For Palmer, who managed only 37 laps and was slowest at the end of day one due to software issues, the Briton enjoyed a more productive morning in the RS16 as he clocked 41 laps.
With Gene Haas looking on for the first time at his new car, Esteban Gutierrez - after a year as Ferrari reserve - returned to the cockpit of an F1 challenger and finished ninth, just over four seconds behind Vettel.
McLaren, whose power unit supplier Honda will have a new boss from March 1 in Yusuke Hasegawa as Yasuhisa Arai is stepping down from the role, managed to rack up 71 laps, with Fernando Alonso posting a 1m27.198s for 10th quickest.
That left Max Verstappen at the rear, with the Toro Rosso driver bringing out the only red flag of the morning when he stopped on track midway through the session with an unspecified problem.
The 17-year-old still managed 59 laps, but was 4.5s behind Vettel.
DAY TWO MORNING TIMES
|2||Daniel Ricciardo||Red Bull/TAG Heuer||1m23.525ss||0.715s||58|
|4||Sergio Perez||Force India/Mercedes||1m25.692ss||2.882s||48|
|11||Max Verstappen||Toro Rosso/Ferrari||1m27.346ss||4.536s||59|