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Delta is now the second-largest U.S. airline by passenger traffic, a common gauge of carrier size, Bloomberg reported Tuesday.

Delta passed United Airlines in 2015 for the first time since United merged with Continental Airlines in 2012. Delta recorded 209.6 billion revenue passenger miles, an industry yardstick of traffic that multiplies the number of passengers by the distance flown. United recorded 208.6 billion revenue passenger miles, the company said in a statement Monday.

American Airlines remains the busiest airline after announcing Tuesday that it flew 223 billion revenue passenger miles in 2015, according to Travel Weekly. 

Adam Hackel, an associate analyst at Sterne Agee CRT, told Bloomberg: “The reality is, Delta offers better service and a better product than United. My first thought was people probably prefer to fly Delta now.”

Delta’s growth abroad may have given it an edge, Raymond James Financial analyst Savanthi Syth told Bloomberg recently. Since traffic is calculated with flight distance, growth overseas can bump up an airline’s standing, she said.

Note: Story was updated Wednesday to include American's 2015 numbers.