Shares in Partygaming, owner of the Partypoker website, have risen 3% as trading opened to members of the public for the first time.
Earnings growth is continuing at Partygaming
Institutional investors have been able to trade the stock since Monday, and the shares, which launched at 116 pence, have risen 23% since then.
The company's shares closed up 10p, or 7%, at 149 pence.
Share prices are rising despite fears about the legality of online gambling in the US, the company's main market.
Partygaming - which was set up by Californian lawyer Ruth Parasol - is based in Gibraltar with no assets in the US.
It is estimated that the majority of its earnings last year came from the US, with Partygaming generating a pre-tax profit of £371m ($665m) in 2004.
The firm's offer price of 116p a share valued it at £4.64bn, the biggest UK stock market debut in five years.
During the first three months of the 2005 financial year earnings growth has continued and sales have almost doubled from the same period a year earlier.