Sebastien Buemi led the times in testing at Jerez on Tuesday as six teams began a three-day session at the Spanish circuit. Buemi, who hopes to land a Toro Rosso race seat for 2009, was half a second quicker than Sebastien Bourdais, who in turn is looking to retain his drive with the team.
Mixed weather saw morning fog give way to intermittently dry and damp conditions, before a late downpour gave the teams the chance to try out their wet-weather tyres. Buemi was among the busiest men on track, the Swiss GP2 star completing 91 laps to Bourdaiss 77 as both ran 2009 downforce levels on the STR3 in combination with slick tyres.
When the rain came, Toro Rosso took the opportunity to compare this years Bridgestone rain tyre with a development version for the 2010 season. Buemi continues testing on Wednesday and Thursday, while Bourdais will hand over to Takuma Sato from Wednesday lunchtime.
The McLarens of Gary Paffett and Pedro de la Rosa were next up, completing just 26 and 21 laps respectively as the team restricted their running in the changeable weather. De la Rosa concentrated on set-up work in the MP4-23A, while Paffett evaluated boost levels in the KERS-equipped MP4-23K. Wednesday will see Heikki Kovalainen back in the cockpit for the first time since the Brazilian Grand Prix.
Beating Kovalainen back to the track by a single day, fellow Finn Kimi Raikkonen made his Ferrari return on Tuesday, the former champion going fifth fastest after 48 laps of set-up and engine work. He will be joined by team mate Felipe Massa on Wednesday.
BMW Sauber had Nick Heidfeld (sixth) and tester Christian Klien (ninth) in action, both in interim F1.08Bs featuring some 2009 bodywork. Kliens car was also fitted with BMWs KERS device, but the Austrians schedule was curtailed after 15 laps following a precautionary engine change prompted by a suspected mechanical problem. Heidfeld, who will be joined by team mate Robert Kubica on Wednesday, managed 49 laps of set-up, suspension and aero work.
After an early visit to the gravel trap, Kazuki Nakajima went on to total 58 laps as he finishes seventh fastest for Williams. Set-up and slick tyre work were the Japanese drivers main focus in the FW30B. Nico Rosberg will continue the teams programme on Wednesday.
At Renault, Nelson Piquet was eighth after a mammoth 124 laps in the R28. The team evaluated 2009 set-ups and slick tyres, as well as putting mileage on their engine in preparation for next seasons three race engine rule. Wednesday will see Fernando Alonsos first winter test outing for the team.
Unofficial Tuesday times from Jerez:
1. Sebastien Buemi, Toro Rosso, 1:18.742
2. Sebastien Bourdais, Toro Rosso, 1:19.288
3. Gary Paffett, McLaren, 1:20.134
4. Pedro de la Rosa, McLaren, 1:20.164
5. Kimi Raikkonen, Ferrari, 1:20.261
6. Nick Heidfeld, BMW Sauber, 1:20.678
7. Kazuki Nakajima, Williams, 1:21.338
8. Nelson Piquet, Renault, 1:21.547
9. Christian Klien, BMW Sauber, 1:22.098
Cosworth's 2004 Champ Car engine 
Formula One looks set to enter an era of standardised engines. The FIA is meeting with teams in Monte Carlo and is expected to approve the use by some teams of a standardised power unit provided by Cosworth, an automotive engineering company, from 2010 onwards. The move to a standard engine, which is common in lower tiers of open wheeled racing such as GP2, was pushed for by FIA President Max Mosley earlier this year as he aims to reduce team costs. This would not see the exclusion of manufacturer made engines, as at this time participation in the system would be voluntary and teams would be free to build licensed Cosworth engines or their own powerplants but on a performance par with the Cosworth unit. Mosley has stated that stabilising Formula One means that the FIA "...must stabilize the system with a base engine which anyone can have and which is inexpensive, as well as a standard gearbox" and has warned of future budget problems, saying that "Honda pulled out because of falling car sales and there is no guarantee that these falling sales, which affect all manufacturers, will not drop further".

Ahead of the meeting of the FIA there have been rumours in the Italian press that Formula One team Renault had broken with the Formula One Teams' Association (FOTA), rumours which Renault has strongly denied. FOTA was established earlier this year by the teams to negotiate with the FIA over cost cutting measures and other changes, changes it hopes will stop the introduction of compulsory standardisation of engines and other parts on F1 cars. The FOTA's position was hard hit last week by the announcement by Honda that they were leaving F1 due to the economic crisis, a move which has caused many teams to re-assert their commitment to a future in Formula One. David Richards, whose Prodrive entry to Formula One was called off last season due to costs, highlighted what he sees as the need for fundamental changes, saying that Honda's exit was 'a salutary lesson for the whole of F1 that things are going to have to change, and everything is going to have to come back a little bit if the whole sport is to prosper in the future'.

Five teams have reportedly expressed an interest in the Cosworth engines from the 2010 season, the five being all four independent teams (Williams, Force India, Red Bull Racing and Scuderia Toro Rosso) joined by manufacturer Renault. If only four teams sign up to the idea, the FIA has announced it will go ahead. Renault have been highly vocal in criticising the failure of the engine development freeze that has existed in Formula One and have, after a couple of seasons of struggling, been under pressure from their parent company to justify the continued expenditure in Formula One. Cosworth have previously been prolific engine suppliers in Formula One, their last stint was supplying engines to Williams in 2006.

The talks come as many of the Formula One teams are in Jerez for part of their winter testing regime, with potential Toro Rosso driver Sebastian Buemi topping the time sheets for the first two days.