Although the rankings measure year-round performances, the in-form players are more likely to be those who have been playing well on the surface going into a Grand Slam. Here's a look at the players with the most ranking points on clay this season heading into the French Open.
It's no surprise No. 1 Novak Djokovic is leading in clay points this year, given the way he has been dominating on all surfaces. The Serb is on a 22-match win streak and won both clay events he played, Monte Carlo and Rome Masters.
The second name could be seen a surprise -- or not. Rafael Nadal has made a habit of winning almost everything in sight on the clay, but this year, he hasn't played up to his standards. The Spaniard is down to No. 7 in the rankings and will be seeded to meet one of the top four in the quarterfinals of the French Open, yet he is still second in points earned on clay this season.
That's partly because he has played six clay events -- more than any of the top players -- and partly because he was a titlist and semifinalist at the South American events in Buenos Aires and Rio. Even if those were taken away, he'd still be fourth with his Monte Carlo semifinal and Madrid final, so it's not like the nine-time French Open champion isn't one of the guys to beat.
His compatriot, David Ferrer, is third, also in large part because of the South American events. As usual, he has been putting up solid results almost every week but is lacking big wins.
The next name would definitely have been a surprise coming into the clay season. Newly married Andy Murray has produced his best clay season of his career, having won Munich and the Madrid Masters to get into fourth place. Murray is second in points won at just the European events.
Into fifth is Tomas Berdych, who has quietly had good performances -- Monte Carlo final, Madrid semifinal, Rome semifinal. He was defeated only by the Big Four players in that stretch.
Berdych is followed by Roger Federer, who had an inconsistent showing but did win the title in Istanbul and reach the final of Rome.
Kei Nishikori has been solid, winning in Barcelona, but hasn't scored a big win against the other top players.
The top seven in clay points are all from the top eight in the rankings, but next come two players who like clay and did well in the South American events. Especially notable is Fabio Fognini, who reached the finals in Rio and has two wins against Nadal on clay this season alone.
In 10th is Stan Wawrinka, who did little until reaching the semifinal of Rome but seems to be playing better.
The names that follow show the stylistic diversity on clay this season, from shot-maker Gael Monfils to big servers in Milos Raonic and John Isner, who are among the top 20 dirt performers.