The quickest times during the six hour practice session were set during the opening hour before the onset of rain.
At the head of the pack were defending champions Allan McNish, Dindo Capello and Tom Kristensen who posted the quickest time at the wheel of the Audi R15.
Scotsman McNish stopped the clock with a best time of 3:30.708, just ahead of the Audi Sport North America car of Lucas Luhr, Mike Rockenfeller and Marco Werner.
The first of the Peugeots featuring David Brabham, Marc Gene and Alex Wurz completed the top three.
The Pescarolo Sport-run Peugeot slotted into fourth place ahead of the Peugeot in the hands of Toro Rosso Formula One driver Sebastien Bourdais.