Mark Webber set the fastest time during final practice for the Canadian Grand Prix.
The 60 minute session was shortened to 30 minutes following barrier repairs due to a heavy accident in a support race.
The session eventually got under way in damp conditions, with Williams's Valtteri Bottas leading the way.
Sauber's Esteban Gutierrez stole top spot but the circuit dried sufficiently for drivers to use slick tyres for the final five minutes of the session.
The rapid rate of the drying circuit meant that several drivers took top spot during the dying moments of the session.
At the end of a frantic five minutes, it was Webber who set the fastest lap time, ahead of Adrian Sutil and Lewis Hamilton.
Daniel Ricciardo was on course for a quick time but spun at Turn 8, while Sergio Perez and Pastor Maldonado also had off track excursions.
