The nine largest U.S. passenger airlines reaped 670 million U.S. dollars in net income in the second quarter of this year, said the U.S. Department of Transportation (DOT) in a report on Tuesday. This indicated a strong recovery because it was a 12.8 percent increase over the same period of last year and much better than the previous quarter\'s loss of 1.72 billion dollars. During the quarter, the United Airlines topped other rivals with 583 million dollars in net income, while American Airlines net lost 263.7 million dollars, according to the report. The top nine airlines also posted an operating profit of 2.3 billion dollars and a 6.0 percent profit margin in the quarter. The United Airlines ranked the first with 583 million dollars in operating profit, while ExpressJet Airlines took the last place with only 4 million dollars. Alaska Airlines enjoyed the highest profit margin of 15.8 percent, compared with ExpressJet Airlines\' 0.9 percent, which was the lowest in the quarter. Operating profit is calculated from operating revenues and expenses, and net income may include non-operating income and expenses, nonrecurring items or income taxes, noted the DOT. The nine airlines are Southwest Airlines, Delta Airlines, United Airlines, American Airlines, US Airways, ExpressJet Airlines, JetBlue Airlines, SkyWest Airlines and Alaska Airlines. All told, these nine airlines carried 80.0 percent of U.S. airlines\' passengers in the second quarter of 2012.