Sebastien Buemi continued to be the man to beat at Jerez as he set the pace for the second successive day of Formula One testing at the Spanish circuit.

Buemi, hotly tipped to secure a race seat with Toro Rosso for 2009, was once again on duty with the senior Red Bull Racing outfit, running alongside Sebastian Vettel for the second day of the test.

Concentrating on set-up work on the 2009 slick tyres, Buemi posted a best time of 1min 17.029secs which saw him end the day three-tenths of a second ahead of Vettel on the times.

"It's been a very good test so far, we've been improving with every lap, which is really good for next season and I'm happy," Buemi said. "We're learning more about the slick tyres too, which is important. I'm looking forward to tomorrow and trying to improve myself more."

Vettel was second quickest despite a number of off-track excursions at turn one but was well clear of Nick Heidfeld in third place for BMW Sauber.

Heidfeld was again at the wheel of a conventional interim car as he collected data for the 2009 season, although his time on track was delayed early in the day due to cold weather conditions.

"After the delay in the morning the weather was nearly perfect, so overall it was a good day for me," the German said. "I did short as well as long runs to compare tyre wear. At the end of the session I did some race start simulations, as this is also an area where we have to adjust to the slick tyres."

Team-mate Robert Kubica was fourth fastest as he worked with the KERS car, while Kazuki Nakajima was fifth for Williams as he worked on set-up, aero optimisation and slick tyre development work ahead of 2009.

"Kazuki was on duty today and took over from where Nico Hulkenberg left off yesterday, continuing with tyre testing and general set-up work," test team manager Dickie Stanford said. We lost a small amount of track time this morning due to the icy weather, but the car has been running well and we've had no other problems. Kazuki will continue in the car tomorrow for our last day of testing this year."

Testing continues tomorrow.