SAN FRANCISCO (MarketWatch) -- Zipcar Inc., the world's biggest car-sharing service, said Tuesday that it has filed the necessary paperwork to launch a public offering that could reap as much as $75 million.

Cars are rented for as little as $7 an hour and come equipped with fuel-purchase debit cards. Residents of dense urban areas typically have multiple Zipcar parking spots within reasonable walking distance.

With the help of Goldman Sachs, Cambridge, Mass.-based Zipcar plans to offer its shares under the ticker symbol "ZIP" and use the proceeds to pay down debt.