The all-Italian Biaggi/Aprilia combination has made considerable progress this season and Biaggi is now constantly in amongst the podium battle. To finish the season with another win would be a major boost for next season, when Max will expect to be one of the title candidates.
As for Rea, the young rider from Northern Ireland has proved himself to be one of the top riders in the category and he will surely be one of the favourites at a circuit where he made his WSBK debut just twelve months ago.
Biaggi and Rea will also be fighting for an overall fourth place, currently in the hands of Biaggi, who has a 14-point lead over his rival.
BSB champion Leon Camier, who will take the start for the second successive race on the Aprilia RSV4 machine, will be looking to impress the Italian team following his first outing at Magny-Cours.
The Noale manufacturer will enter three bikes, with Shinya Nakano returning for the first time since the Nurburgring.
Also searching for a place next year will be Britain's Shane Byrne (Sterilgarda Ducati), who may represent an outsider at Portimao.
In last year's pre-season testing he surprised everyone by setting the best time and will surely be looking to end this season on a high note - as will fellow Brit Leon Haslam, who starts his last weekend at Stiggy Honda before switching to Alstare Suzuki.
Just days after the 2009 season ends, a test session at Portimao will mark the start of preparations for the 2010 season - including an early debut for Haslam's team-mate Sylvain Guintoli in the Alstare team (in place of Max Neukirchner) and James Toseland's first ride on the R1.
The title is also still up for grabs in the World Supersport Championship, with Cal Crutchlow (Yamaha World Supersport) 19 points ahead of Eugene Laverty (Parkalgar Honda).
The English rider needs just a tenth place, irrespective of what his adversary does, to be crowned champion, before heading up to Superbike next year, when he will team up with Toseland in the official Yamaha squad.
As well as the Riders' title, Crutchlow will also have one eye on the Manufacturers' crown as Yamaha are just one point behind Honda.