Tennis is the most popular sport with punters after horse racing and soccer, the general counsel for the internet betting exchange Betfair said on Monday.

David O'Reilly told a seminar on Integrity on Sport hosted by the London law firm Charles Russell that betting on tennis was particularly popular in central and eastern Europe where there was no culture of sports gambling.

"The key factors are technology and television," O'Reilly said. "It's truly global. Tennis betting is the third most important after horse racing and soccer."

Last August, Betfair voided all wagers on a second-round match at the Sopot Open in Poland between defending champion Nikolay Davydenko and Argentine Martin Vassallo Arguello because of what is said were irregular betting patterns.

Davydenko won the first set but then retired with a foot injury when his opponent, then ranked about 80 places lower, was leading 2-6 6-3 2-1.

The Russian, ranked fourth in the world, again denied this month being involved in match-fixing or illegal gambling. The governing body of men's tennis (ATP) is investigating the match.

"This was probably the most extreme case of betting patterns that we have ever seen," O'Reilly said. "If customers feel the sport isn't clean then we lose their business."

O'Reilly said there was no formula for detecting suspicious betting patterns.

"It's not a science, it depends on numerous factors," he said. "It depends on how the market is reacting. It's a combined art and science, it's not possible to be definite."

(Agencies via China Daily January 23, 2008)