The US airline industry continues to see a strong upward trend in demand for air travel, with the top 10 carriers remaining unchanged from last month. These airlines collectively dominate the market, shaping domestic and international travel trends.
American Airlines remains the largest US airline, holding a 21% market share with 21.8 million seats in March 2025. Southwest Airlines and Delta Air Lines follow closely behind, controlling 19% and 18% of the market, respectively.
Meanwhile, Allegiant Air reported the largest percentage increase in capacity, increasing by 22% year-over-year, while Spirit Airlines experienced a 12% decline, losing 540,500 seats compared to March 2024.
In this article, let’s explore the top 10 busiest airlines in the US this month.
Busiest US Airlines in 2025
Photo: Clément Alloing1. American Airlines (AA)
American Airlines (AA) retains its position as the largest carrier in the United States, offering 21,761,191 seats this month.
As the primary carrier at Dallas/Fort Worth International Airport (DFW), Charlotte (CLT), Miami (MIA), and Chicago O’Hare (ORD) among others, AA benefits from a robust hub-and-spoke network. Its extensive network connects passengers to more than 350 destinations worldwide.
In recent years, AA has been focusing on fleet modernization, introducing new Boeing 787 Dreamliners and Airbus A321neos to enhance efficiency and expand long-haul capabilities.
Photo: Clément Alloing2. Southwest Airlines (WN)
Southwest Airlines remains the second-largest airline in the US, offering 19,805,220 seats in March 2025. With a 19% market share, it continues to be a dominant force in domestic travel.
Unlike traditional hub-based airlines, Southwest operates a point-to-point network, with major operations at Denver (DEN), Las Vegas (LAS), and Phoenix (PHX). Its low-cost model and two-free checked bags policy have attracted leisure and business travelers alike.
However, the LCC will modify its attractive baggage policy starting May 28, 2025. Rapid Rewards A-List Preferred Members and Business Select fare customers will continue receiving two free checked bags, while A-List Members will receive one free checked bag.
Moreover, Rapid Rewards Credit Card members will receive credit for one checked bag. Customers not qualifying for these options will pay for their first and second checked bags.
Delta Air Lines Airbus A50 with 100 Years Livery | Photo: Clément Alloing3. Delta Air Lines (DL)
Delta Air Lines (DL) continues to hold the third-largest market share in the US, with 19,094,843 seats this month, representing 18% of total capacity. Known for its strong customer service and operational reliability, Delta continues to be a preferred choice for many travelers.
With major hubs in Atlanta (ATL), New York (JFK), and Detroit (DTW), Delta has a well-balanced domestic and international network. The airline has also been expanding its presence in premium travel markets, investing in new products and lounges.
Delta’s fleet renewal program includes more Airbus A321neos, A330neos, and A350s, focusing on fuel efficiency and sustainability goals.
4. United Airlines (UA)
United Airlines (UA) ranks fourth among US carriers, offering 16,758,484 seats this month. The airline’s extensive hub network at Chicago O’Hare (ORD), Denver (DEN), and Houston (IAH) makes it a major carrier in both domestic and global markets.
The Chicago-based carrier has been expanding its international long-haul routes, especially to Asia and Europe, leveraging its Boeing 787 and 777 fleets. The airline’s United Next initiative is also driving domestic growth, with additional Boeing 737 MAX and Airbus A321neo aircraft on order.
Photo: Clément Alloing5. Alaska Airlines (AS)
Alaska Airlines is the fifth-largest US airline, with 4,530,103 seats in March 2025. The airline’s network is centered around the West Coast, with key hubs in Seattle (SEA), Portland (PDX), and San Francisco (SFO).
Alaska’s strategy focuses on strong regional connectivity, particularly in the Pacific Northwest and Alaska, while also expanding transcontinental routes. Its partnership with the Oneworld alliance and codeshare agreements with American Airlines have further strengthened its market position.
6. Spirit Airlines (NK)
Spirit Airlines, a leading ultra-low-cost carrier (ULCC), has 3,967,513 scheduled seats this month. However, its capacity has declined by 12% year-over-year, reflecting network adjustments and reduced demand in certain markets.
Despite the cutbacks, Spirit remains a popular budget carrier, with key operations in Fort Lauderdale (FLL), Orlando (MCO), and Las Vegas (LAS). The airline continues to focus on ancillary revenue, offering unbundled fares that allow passengers to pay only for the services they need.
Photo: Judah Davis | Shared on X7. Frontier Airlines (F9)
Frontier Airlines maintains its position as one of the top 10 US carriers, with 3,854,276 seats on offer this month. Like Spirit, Frontier follows the ultra-low-cost carrier model, focusing on leisure travelers.
The airline’s major bases include Denver (DEN), Orlando (MCO), and Las Vegas (LAS), with an emphasis on low-fare, high-density routes. Frontier has also been expanding its seasonal and secondary airport services, targeting underserved markets.
New Airbus A320neo and A321neo aircraft are helping the airline improve operational efficiency and reduce costs, allowing it to stay competitive in the low-cost segment.
8. JetBlue Airways (B6)
JetBlue Airways ranks eighth, with 3,563,786 seats in March 2025. The airline has its operations centered in New York (JFK), Boston (BOS), and Fort Lauderdale (FLL), operating a bulk of domestic and a handful of international routes.
Known for its premium economy-style experience, JetBlue continues to expand its Mint business class on transcontinental and transatlantic routes. The airline has been operating flights to multiple European destinations including London, Paris, Dublin, and Amsterdam, increasing its global footprint.
Photo: Clément Alloing9. Allegiant Air (G4)
Allegiant Air saw the largest percentage increase in capacity among the top 10 carriers, with a 22% growth year-over-year, reaching 2,309,908 seats this month.
Focused on low-cost, leisure-focused travel, Allegiant operates point-to-point routes between smaller cities and vacation destinations like Las Vegas, Orlando, and Phoenix. The airline’s unique model keeps costs low while serving niche markets.
New aircraft deliveries, including Boeing 737 MAX jets, will further enhance Allegiant’s ability to expand into new markets.
10. Hawaiian Airlines (HA)
Hawaiian Airlines rounds out the top 10 with 1,148,713 seats in March 2025. The airline dominates inter-island and mainland-to-Hawaii routes, with a strong presence in Honolulu (HNL) and Kahului (OGG).
Its new Boeing 787-9 Dreamliners will support long-haul expansion, particularly in the Asia-Pacific region. Hawaiian continues to thrive despite competition from larger carriers.
Photo: ca350 | FlickrConclusion
The Top 10 busiest US airlines continue to dominate the US market, with American Airlines maintaining its position as the largest carrier, holding 21% of total capacity. Southwest and Delta remain close competitors, underscoring the strength of the country’s three largest airlines.
While most carriers saw stable capacity, Allegiant Air led in growth with a 22% increase, while Spirit Airlines faced a 12% decline as it adjusted its network strategy. These shifts highlight the dynamic nature of the airline industry as carriers respond to changing market conditions.
With ongoing fleet expansions, strategic network adjustments, and competitive market dynamics, the rankings of the busiest US airlines will continue to evolve, reflecting the ever-changing landscape of air travel.
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