National car sharing services Zipcar and Flexcar announced their merger today. The combined companies, which have 180,000 members and a national fleet of 5,000 cars in 8 major cities, will be based in Cambridge, Mass. when the merger is complete this week. The financial terms of the deal were not disclosed. The combined company will be called Zipcar, and one of its three largest investors will be D.C.-based Revolution LLC, owned by America Online's founder Steve Case. Revolution bought a controlling stake in Flexcar in 2005. As for going public, the executives said they have enough capital resources and an initial public offering is not imminent. The companies said they see a potential for 2 million users in the U.S. and 7 million worldwide.