Zipcar, the world's largest car-sharing company, raised $174.3 million in its long-awaited initial public offering (IPO) on April 14. Under the symbol ZIP, shares opened at $18 and rose to $28 by the close of the first day of trading, about 30 percent higher than initially sought.

In an SEC filing in March, Zipcar priced its IPO at $14 to $16, which was expected to net the company $89 million to $95 million on sales of 8.3 million shares on the Nasdaq.

Zipcar reported $186.1 million in worldwide revenues in 2010 on a fleet of about 8,000 vehicles, though the company has yet to turn a profit. "The success of the Zipcar IPO is certainly an indication that car sharing is attracting interest outside of the traditional transportation sectors, which makes sense given the disruptive nature of the business model," said Dave Brook, publisher of a carsharing industry blog and consultant with Team Red US. "Now that they're public they have their work cut out to grow the business even more - and start making a profit."

At the end of trading on Tuesday, April 19, Zipcar closed at $29.27.