Preview - Portuguese Grand Prix.

The Iberian peninsular plays host to its third, and Portugal's first, MotoGP this weekend, with all riders heading into something of an unknown.

The Estoril circuit, once a stalwart of the Formula One world championship, has been redesigned and rebuilt in the hope of attracting Bernie Ecclestone's circus back to Portugal once more, but has landed a round of the MotoGP series into the bargain. A pre-season test there provided the riders with an early taste of what they can expect this weekend, but the escapade still remains one of mystery.

The man who came out on top of that test is the same man who leads the championship standings as the series returns to Portugal. Kenny Roberts, despite finishing only fourth in the last round of the series at Brno, nevertheless managed to increase his lead over the best placed challenger, Valentino Rossi, but is well aware of the Italian rookie's potential.

Forty-two points separate the pair going to Estoril but, since winning his maiden race in the GP500 category at Donington Park, Rossi has looked the more likely to make it onto the top step of the rostrum in recent races. Roberts still holds the edge in terms of wins - three to one - but Rossi has finished second in each of the last two races, with the American third and fourth respectively.

Roberts puts a lot of the results down to the fact that his Suzuki has not been best suited to the tracks used over the last couple of months, but claims that those still to come on the schedule should suit the temperamental machine. He is also well aware, however, that he merely needs to keep the bike on the road, and near the front, if he is to repel Rossi's late threat.

The Italian himself can hardly believe that he is in a position to challenge for the title in his first year, especially one in which the works Hondas have singularly failed to shine. Surprisingly, therefore, it is the privateer, or semi-works, machines of Rossi and Pons twins Alex Barros and Loris Capirossi which have taken the fight to early season pace-setters Roberts and Carlos Checa.

Checa, however, looks less and less likely to feature in the title fight, as one poor weekend in Catalunya seems to have brought back all his old frailties. The Spaniard, having hardly scraped fairing on floor all year, now appears incapable of going through a meeting without at least one crash, and his lacklustre form frequently means that he has to battle through the field from poor qualifying spots on race day.

The Pons boys, however, seem to be holding their form a little better - despite all the setbacks that have befallen them. Barros is a two-time winner this season, including that nail-biter with Rossi at the Sachsenring, but endured a rare bad weekend in the Czech Republic, where he fell in the race.

Team-mate Capirossi is rapidly proving himself to be the iron-man of the MotoGP paddock, having now broken both hands this season. His heroic ride to the rostrum in Holland could not be repeated at Brno, however, where the Italian collapsed in agony after struggling to fifth with his injuries taped up for strength. Although he has had a two-week break to get over the worst of the pain, it may be that Capirossi does not feature predominantly at Estoril, which will be disappointing in his 150th GP.

This will be manna for Roman rival Max Biaggi, who appears to be on something of a roll after winning last time out. The self-styled Roman Emperor was in a class of his own at Brno, even having time to pop wheelies for the crowd halfway around his final lap. His form is going in the opposite direction to team-mate Checa's and could be enough for Biaggi to become the thorn in the side of the championship contenders.

Given that this is perhaps the most competitive GP500 campaign for several years, there are others who will want a say in how the title is decided and, at a new venue such as Estoril, this weekend could be their chance to shine.

It is odd to say that the Repsol riders could act as spoilers in Portugal but, such is their woeful showing this year, Alex Criville, Sete Gibernau and Tady Okada cannot be expected to be regular front-runners for the rest of the year. The reigning champion has already signed up for another year with the squad, but his two team-mates will be riding for their livelihoods on Sunday. Okada is heavily tipped to retire or opt for the superbike route, but Gibernau is desperate to secure a seat for 2001.

Another man facing the axe if his performances do not shape up in the coming races is Red Bull Yamaha's Regis Laconi. A race winner twelve months ago, the Frenchman has been comprehensively outshone by team-mate Garry McCoy this year, resulting in the little Australian being offered a new deal with the WCM outfit, but Laconi looking anxiously over his shoulder.

Jeremy McWilliams and Tetsuya Harada are two of those who may be in a position to take the seat from Laconi, if only because Aprilia continues to debate its own future in the class. Neither rider has done badly this year, but it is symptomatic of McWilliams' luck that the best bike he has ridden may be taken from underneath him. The Irishman is another who would rather stay in MotoGP than go to superbikes next year, and will be looking to impress on 'neutral' ground this weekend.

Finally, the Modenas team tested both Mark Willis and flying Dutchman Jurgen van der Goorbergh at Brno immediately after the grand prix there and, although it looked set to Luca Cadalora who saw out the season on board Kenny Roberts' Sr's machine, this weekend will see Willis in the hot-seat.

The GP250 series looks likely to be the domain of Chesterfield Yamaha once again, but not if Tohru Ukawa has anything to do with it. The Japanese GP500 hopeful won at Le Mans when the series returned there this year, and also took the flag in tricky conditions at Assen, so can be relied upon to provide the biggest challenge to series leaders Olivier Jacque and Shinya Nakano. Seven points separate the two silver bikes as they head for Portugal, but Ukawa is just slightly further back, and still retains title hopes.

While these three go for the crown, however, there will be others equally keen to upset the formbook and take the race win. Ralf Waldmann did just that in poor conditions at Donington Park, but has failed to shine elsewhere, while Ukawa's team-mate Ant West is fervently hoping that the pre-season test at Estoril will play into his hands after successive tenth-place finishes in the past two races. With all riders facing the unknown, however, Japanese rookie Daijiro Katoh will feel that he is competing on more of an level playing field, and could do well. Likewise, British riders Jamie Robinson and Jay Vincent will be looking to build on recent good performances, and may be the ones to mix it at the front.

In GP125, things looked a little more clear-cut heading to Brno - and then Roberto Locatelli beat Youichi Ui in a straight fight. Until that point, the little Derbi rider had set the precedent of winning if he stayed onboard, and began to appear a dead cert for the title. Now, however, Locatelli has closed the gap and, along with Brno podium visitor Emilio Alzamora, remains in the championship picture.

Erstwhile series leader Mirko Giansanti, Benetton team-mate Masao Azuma and the effervescent Nobby Ueda look likely to be the main threats to this trio, with Arnaud Vincent, Simone Sanna and Lucio Cecchinello also capable of springing a surprise result.