The US internet radio service Pandora Media rose sharply on its debut on the New York Stock Exchange, before falling back.
The firm, which has yet to make a profit, had an offering price of $16 (£9.76) a share.
It rose as high as $26 a share on Wednesday before settling down to around $18.75.
The share price values the company at about $3bn, which is well above the current value of AOL, for example.
Pandora is the latest in a series of high-profile internet share sales, with LinkedIn already having floated and Groupon planning a listing.
LinkedIn has a market capitalisation of about $7bn.
Facebook is also expected to launch on the stock market in the next year.
Pandora started out as a music recommendation service called Savage Beast Technologies in 2000.
It changed its name in 2005 when it launched an internet radio service, which allows users to create custom radio stations by specifying which artists and genres they want to hear.
It has 94 million registered users and makes most of its money through advertising.