United, Continental Merger Closes

United and Continental airlines officially closed their $3.2 billion merger on Friday, extending the consolidation of the U.S. aviation industry and creating the largest cargo-carrying passenger airline in the United States.

United said in a statement that consolidating operations will be “complex” and take 12 to 18 months.

The new United Continental Holdings becomes the largest airline in the world and will operate the United and Continental networks separately until the fleet, crew, maintenance and other operations can be blended together.

By The Numbers: U.S. Domestic Air Cargo.

The combination will make United Continental by far the country’s largest cargo carrier among the combination airlines. United and Continental had a combined $560 million in cargo revenue in the first half of 2010, while Delta Air Lines counted $387 million in belly freight business.

The airline, which is based in Chicago and led by former Continental Chairman and CEO Jeff Smisak, also faces the prospect of combining domestic U.S. hubs. Continental has operated through Houston and Newark, N.J., while United has large hubs at Chicago, Denver and Washington Dulles.

The merger brings the number of U.S. major combination airlines to six, down from 10 the country had a little more than a decade ago.