Red Bull driver Daniel Ricciardo set the fastest time on a slippery track in the final practice session at the Chinese Grand Prix as the other top drivers limited their running due to the wet weather.
Ricciardo completed his lap around the Shanghai International Circuit in 1 minute, 53.958 seconds, about 0.5 seconds faster than Felipe practise of Williams in second. Lotus driver Romain Grosjean set the third-fastest time of the morning.
Mercedes drivers Lewis Hamilton and Nico Rosberg and Ferrari's Fernando Alonso did not set a timed lap in the session, spending much of the time in the garage.
A fine rain fell throughout the morning, with more showers predicted for the qualifying session in the afternoon.
It looks likely to be the third wet qualifying session of the F1 season, following the rainy conditions in Australia and Malaysia, with both poles won by Hamilton.
Mercedes looking strong
Mercedes looks to be the team to beat again in the qualifying session after posting fast times on the track in the previous practice, though Alonso, Ricciardo and four-time defending world champion Sebastian Vettel were not far off the pace.
Vettel complained of clutch slip and a lack of acceleration during his runs and managed no better than 11th. His team said it appeared to be a KERS problem and they would try to correct it before qualifying.
Lotus driver Pastor Maldonado also ran into mechanical problems, pulling off the track midway through his 13th lap and walking back to the garage. He set the sixth-fastest time of the morning before stopping.
It's been a tough season and a trying week so far for the Venezuelan, who crashed into the wall on his way into the pits on Friday and also spun his car after looking down briefly to adjust the settings on his steering wheel.
He carries a five-place grid penalty into this the next race for flipping Esteban Gutierrez's Sauber at the Bahrain GP two weeks ago.