AT&T is the leading Internet Service Provider for businesses in the United States, handily beating out rival Verizon.

AT&T has a 20 percent ISP market share in the segment, according to a report released Monday by digital research firm comScore. Verizon had a 12 percent share, and CenturyLink (which recently merged with Qwest Communications) held a 7 percent share.

The Dallas-based company led the market in its hometown, as well as in Los Angeles, Chicago and Philadelphia, among other cities. Verizon led the New York market with 20 percent.

Other companies in the top 10 include Comcast, Time Warner Cable, Sprint Nextel and Cox. The top 10 companies control 71 percent of the ISP market among businesses. Among large businesses, that number rises to 85 percent.

The current state of the domestic business ISP market reveals a landscape led by a couple of top providers, Greg Mishkin, comScore Vice President of Telecom and Wireless said in a statement.

However, even with small business carriers contributing only a fraction of the traffic delivered by top carriers, the business ISP market is still more competitive than the residential ISP market.

AT&T is the largest telecommunications company in the United States as it garnered $124.3 billion in revenue for 2010. Verizon is the second largest, with 2010 revenue totaling $106.6 billion.