Zynga Inc shares opened as much as 10 percent above their offer price on Friday, but then rolled back showing that investors were still concerned about its dependence on Facebook and its growth prospects.

Analysts and investors had expected Zynga, maker of Facebook games, to raise its price or boost the number of shares it was selling, since demand had appeared strong in recent weeks.

Shares of Zynga were down 2.6 percent at $9.74 in early trading, but in the opening minutes of trading on the Nasdaq, the stock rose 10 percent to $11.00.

The company, which competes with Electronic Arts, sold 100 million shares of Class A common stock at $10 per share in the IPO, roughly 11 percent of its shares on a diluted basis, at the top end of the $8.50 to $10 indicative range.

Zynga wants to avoid what happened to Groupon Inc, another closely watched Internet IPO that rose on its first day of trading in November but slumped below its $20 issue price about three weeks later

Zynga's IPO had been highly anticipated because it is seen as a way for investors to get a slice of Facebook's growth before the social network itself goes public. About 95 percent of its revenue comes from Facebook, where it makes money from selling virtual items such as virtual jewelry and poker chips in its games.

Unlike Groupon, Zynga is profitable, but less than 3 percent of its players spend money on items in its free games.

At $1 billion in proceeds, Zynga's IPO would still be the largest from a U.S. Internet company since Google Inc raised $1.9 billion in 2004.

(Reporting By Liana B. Baker)