ATLANTA, Jan. 12 (UPI) -- Delta Air Lines nudged its way up in 2015, becoming the second-largest American carrier in terms of traffic, statistics showed Tuesday.
American Airlines remains No. 1 with 223 billion revenue-passenger miles in 2015.
Atlanta-based Delta reported that its fleet flew just under 210 billion revenue-generating miles for the year -- narrowly topping United Airlines, which flew 208.6 billion miles, by comparison.
"The reality is, Delta offers better service and a better product than United. ... People probably prefer to fly Delta now," analyst Adam Hackel said.
Hard-charging Southwest Airlines continued its occupation of the No. 4 spot, with 117.5 billion miles flown in 2015 -- but recorded the greatest year-to-year increase of all the carriers, nearly 9 percent. JetBlue and Alaskan followed in fifth and sixth.
Delta's 2015 performance marked a 3.3 percent increase over the year before -- more than twice the growth United saw.
Delta has made substantial strides in recent years after filing for bankruptcy protection in September 2005, reorganizing the airline and emerging from bankruptcy in early 2007.
Meanwhile, United is working to streamline its 5-year-old merger with Continental, saying it is "continuing to focus on running a reliable operation and investing in the tools and services that allow us to deliver the flier-friendly experience our customers deserve and expect."
Delta climbed to first place in miles flown after its 2008 merger with Northwest but relinquished the title to United after its merger in 2010. American trumped both in 2014 following its acquisition of US Airways.
Delta did not formally comment on its ascension to the No. 2 spot -- which is the first time it has done so since United's takeover of Continental.
The number of miles flown is one of the key statistics used to gauge competition in the airline industry. The number of passengers carried is also cited in airline rankings. For 2015, Delta finished second in this metric, as well, recording more than 174 million fliers. American was first, with 201 million, and United's 140 million earned it fourth place, behind Southwest.
American, Delta, United and Southwest account for more than 80 percent of domestic air traffic.