I have chosen to answer this question in terms of the biggest amount of scheduled passengers. Southwest Airlines in the United States serves a relatively small geographic region. In 2007, they carried almost 102,000 passengers. In fact, the top 4 airlines in terms of scheduled passengers are all American: Southwest, American, Delta and United. Southwest’s main terminal is in Las Vegas, but the airline services almost every state in the Continental U.S. including those in the Eastern U.S.

American Airlines has the largest fleet of planes at 655 aircraft, followed by Air France/KLM at 589 aircraft. Ryanair, an Irish airline is headquartered at London’s Stansted terminal and serves the most international passengers. Ryanair has a notorious reputation for poor customer service, inappropriate and offensive advertising, and discrimination against handicapped passengers. They have been forced to pay damages in many cases. The executive staff of Ryanair seem to thumb their noses at attempts to tame their advertising or change their policies.