• United Airlines grew its second-quarter profit thanks to strong travel demand, especially in international markets.
• United and Delta have been standouts in an airline industry awash in U.S. domestic capacity.

United Airlines' second-quarter profit rose more than 20% from last year as strong demand for international travel boosted the carrier's results, but its third-quarter forecast came in shy of estimates as an oversupply of flights weighs on fares.

United said Wednesday that it expects to earn between $2.75 and $3.25 a share on an adjusted basis in the current quarter, lower than the $3.44 a share analysts polled by LSEG estimated.

Here's what United reported for the second quarter compared with what Wall Street expected, based on average estimates compiled by LSEG:

• Earnings per share: $4.14 adjusted vs. $3.93 expected
• Revenue: $14.99 billion vs. $15.06 billion expected

United earned $1.32 billion, or $3.96 per share, in the three months ended June 30, up from $1.08 billion, or $3.24 per share, a year earlier. Adjusting for one-time items, it reported earnings of $4.14 a share, compared with $3.93 that analysts expected.

Revenue of $14.99 billion jumped 5.7% from the year-earlier period, though it was just shy of estimates.

United reiterated its full-year forecast for adjusted earnings of $9 to $11 a share.

"Looking back at the quarter now, it is increasingly clear that demand was in fact strong, it just could not keep up with the incremental industry domestic capacity added in 2024. Excess capacity, in turn, pressured yields," United Chief Commercial Officer Andrew Nocella said during the company's earnings call.

United and Delta Air Lines, which also disappointed with its third-quarter guidance, have still been standouts in the U.S. airline industry. Most carriers have been struggling with an increase in domestic capacity that has weighed on airfares, despite the record demand.

Both carriers have added international flights, which have been in high demand after the pandemic, and premium offerings, like bigger lounges and more spacious seats, capitalizing on travelers willing to pay more for a ticket.

United said on Wednesday that premium revenue grew more than 8% from last year, while sales from the most restrictive basic economy tickets rose 38%, as it works to cater to both ends of the market.

The company expanded domestic flying by more than 5% in the second quarter over last year, and unit revenues fell more than 1% over last year. Yields on flights to and from Europe, which is a smaller slice of United's sales, rose more than 5%, compared with the second quarter of 2023.

United CEO Scott Kirby said airlines have been trimming their schedules and that there will be an inflection point to moderate the supply in mid-August.

"I've been through these cycles with capacity many times in my career, this is the fastest respond and it's also the biggest gap between the leading airlines and the other airlines, which I think is part of the reason the response is so fast," Kirby said Thursday during the earnings call.

On Tuesday, Spirit Airlines cut its second-quarter forecast, citing weaker-than-expected revenue for fees like seating or luggage. Southwest Airlines and American Airlines, which report results on July 25, previously reduced their second-quarter estimates.

— CNBC's Ece Yildirim contributed to this report.