Car Sharing start-up Zipcar has raised another $10 million to finance expansion.

"The company had previously raised about $10.5 million in three angel rounds, with about 45 individual investors, bringing the current total to more than $20 million. But Zipcar CEO Scott Griffith said the latest venture round could expand to $15 million, depending on how the company's expansion plans work out.

Zipcar, which has more than 40,000 members and nearly 600 vehicles, currently has services in Boston, New York City, and Washington, D.C. It also has partnerships with university campuses in north carolina and California.

Zipcar is profitable in all of its markets, according to Mr. Griffith."

European companies and public entitities have poured millions into similiar projects in Europe. Hardly one is profitable. I wonder what is Zipcars success recipe?