UAL said its loss amounted to $152 million, or $1.32 a share, compared with a year-ago profit that was exaggerated by $22.9 billion in bankruptcy reorganization items.
The airline exited bankruptcy in February 2006, and year-over-year financial comparisons are skewed by accounting related to that. UAL also issued new shares on its emergence from bankruptcy in February 2006.
Excluding the reorganization items, UAL said it lost $237 in the first quarter, compared with a loss of $311 a year earlier.
"Mild disappointment," said Calyon Securities analyst Ray Neidl. "Not as bad as it looks. They are adjusting for their frequent flyer program. That probably accounted for a third of that loss."
UAL is the first major airline outside of bankruptcy to report a loss in the first quarter. Rival AMR , parent of American Airlines, posted a profit last week, reversing a year-ago loss.
The airline industry has been battered in recent years by low-fare competition and high fuel costs. Carriers have been in recovery mode, however, thanks to strong demand and higher fares.
UAL's revenue declined to $4.4 billion, from $4.5 billion a year earlier.
UAL said a new deferred revenue accounting policy for its Mileage Plus program reduced its quarterly revenue by $107 million. The airline also estimated that cancellations due to winter storms reduced passenger revenue by about $32 million.
The company ended the quarter with cash and short-term investments worth $4.2 billion, including $856 million of restricted cash.
Since exiting bankruptcy, UAL has focused on cost cuts. The airline paid $1.04 billion for fuel in the first quarter, down from $1.07 paid in the comparable year-ago period. Jet fuel is the airline second biggest expense after labor.
"We continue to generate significant cash flow by tightly controlling costs and improving ticket revenue growth in a seasonally weaker quarter," UAL Chief Executive Glenn Tilton said in a statement.
Shares of UAL fell 14.8% in the first quarter, outpacing the Amex airline index, which fell 9.8% in the quarter.