Sources close to the negotiations said the float is already oversubscribed by top institutional investors within its £11 to £14 price range.
It is understood at least one major investor has increased its offer from £12.50 a share to £13.75 a share.
Around 10 per cent of the stock will be floated in the IPO, with final pricing due to be announced on Friday. If it achieves the expected pricing, Betfair will crash straight into the FTSE 250 index.
Betfair declined to comment.
The gambling exchange was launched 10 years ago by Andrew Black, an ex-professional gambler, and former JP Morgan trader Edward Wray, who jointly own one quarter of the group. The company cuts out traditional bookmakers by matching individual gamblers.
Meanwhile, Betfair’s punters have placed Wayne Rooney odds-on to leave Manchester United during the January transfer window following his acrimonious bust-up with manager Alex Ferguson.