Red Bull driver Daniel Ricciardo topped the timing sheets while Ferrari and McLaren - in the 2015 cars - racked up almost 300 laps on the opening day of Pirelli wet-tyre testing at Paul Ricard Circuit in southern France.
Recycled water was used to wet the track, after which the cars were unleashed from 9:00am onward. Each team doing 10 lap stints.
Ricciardo, Kimi Raikkonen (Ferrari) and Stoffel Vandoorne (McLaren) were on duty as they put the Pirelli prototype wet compounds to the test.
The three teams combined to rack up 285 laps, with only one stoppage during the course of the day when Vandoorne's McLaren cam to a halt out on track with an engine issue.
Vandoorne said, "We had an engine failure. The team asked me to stop the car, so that was the end of our day. All teams were running last year's engines. We were planning to change it overnight, but unfortunately it broke at the end of the day."
Ricciardo racked up 99 laps and in the process set the best time of 1:08.713, almost half a second up on Vandoorne with 87 laps completed and Raikkonen also with 99 laps to his credit, a second down on the top time.
Raikkonen said at the end of the day, "It was like a normal day of testing. I think it’s too early to say much about these prototype tyres, but it was a very useful session, because everyone was running under the same conditions."
"It’s been a while since we’ve driven and, even if it was just one day, there’s always something you can learn from it," added the Finn.
On Tuesday, the final day of the two day test, will see Vandoorne again in the McLaren cockpit, with Sebastian Vettel replacing Raikkonen in the Ferrari and Daniil Kvyat on duty for Red Bull.