Ruben Xaus kept Castrol Honda at the top of the World Superbike timesheets during the fifth of six test sessions at Portimao, though poor weather conditions continued to hamper proceedings.

Following rain earlier in the morning, chilly temperatures prevented the circuit from drying effectively, with a short period towards the end of the session proving the only realistic opportunity to set a representative lap time.

Only Xaus and Michel Fabrizio took the chance, Xaus slashing seconds off a previous best set by Sylvain Guintoli to come out with a 1min 47.065secs. Fabrizio was a second further back on his Suzuki, but then six seconds ahead of Marco Melandri - who ventured out for just two laps right at the end of the session - in third.

Guintoli was fourth fastest, ahead of Ducati counterpart Carlos Checa, while Tom Sykes and Joan Lascorz put in some useful laps for Kawasaki in sixth and seventh.

All but Eugene Laverty and Max Biaggi made it out onto the circuit, though most for only for a brief time, with Jonathan Rea, Noriyuki Haga and Ayrton Badovini completing the top ten.

With just a single day of dry mileage under their belts, the riders now have just one more session to come this afternoon.