India's Narain Karthikeyan pressed his claims to be Williams's reserve driver next season by testing for the Formula One team in Spain on Wednesday.
The Chennai driver, who raced for Jordan this year but has failed to find a place for 2006 with what is now the Midland team, set the fifth fastest time of the day at the southern Jerez circuit.
Williams said he did 49 laps with a best time of one minute 20.291 seconds, faster than German rookie Nico Rosberg who has secured the team's second race drive alongside Australian Mark Webber.
Rosberg lapped in 1:20.644.
Williams technical director Sam Michael did not comment on Karthikeyan's performance, saying only the Indian had "spent time familiarising himself with the car, carrying out long runs, systems checks and calibration work".
The team, who finished fifth in the constructors championship this year, have yet to appoint a test and reserve driver for 2006.
Karthikeyan is one of several drivers with race experience in the frame.