As the commercial aviation industry has changed over the past several decades, the United States domestic airline market has grown to become one of the most competitive and complex in the world. The market serves hundreds of millions of passengers each year across a vast network of cities. Yet despite the sheer number of carriers based in the United States, a small group of major airlines controls the majority of market share.
These major carriers provide reliable schedules and frequent flight options to travelers around the US. Each carrier has a slightly different approach to serving this market. Let’s take a closer look at the nine major airlines that are dominating the US market share.
Allegiant Air
The airline is flying just under 10,000 flights in October 2025.
Credit: Shutterstock
Allegiant Air is a prominent low-cost airline that is headquartered in Las Vegas, Nevada. The company was founded in 1997, and began service the following year. Allegiant Air has expanded significantly over the years, operating several bases across the United States. This includes its bases at Harry Reid International Airport (LAS), Destin-Fort Walton Beach Airport (VPS), Cincinnati-Northern Kentucky International Airport (CVG), Nashville International Airport (BNA), and Orlando Sanford International Airport (SFB), among others.
The airline flies a small fleet of around 132 total aircraft. It primarily operates narrowbody aircraft, as it transports passengers on domestic flights across the US. According to ch-aviation, the airline operates the following aircraft:
Aircraft Type
Total Active Aircraft
Airbus A319-100
32
Airbus A320-200
84
Boeing 737-8-200
16
The airline remains a significant force in the US. Allegiant Air aims to serve primarily leisure travelers, transporting passengers from northern US cities to warm-weather tourist destinations. It also serves smaller destinations with fewer direct flights from other major carriers, avoiding competition from larger airlines. According to Cirium, in October of this year the airline will operate a total of 9,638 flights with the capacity to serve just over 1.7 million passengers.
Spirit Airlines
The airline is flying just under 12,000 flights in October 2025.
Credit: Shutterstock
Another popular airline in the domestic US is Spirit Airlines. The company as an airline can be traced back to the 1980s, when it was a Detroit, Michigan-based charter company. However, it began scheduled commercial flights in June 1992. Currently, the company is based out of Fort Lauderdale Hollywood International Airport (FLL) in Florida, although it operates out of several other airports, such as Newark Liberty International Airport (EWR), Hartsfield-Jackson Atlanta International Airport (ATL), and Chicago O’Hare International Airport (ORD), among others.
Spirit Airlines operates only narrowbody aircraft in its fleet, and the airline currently only flies Airbus aircraft. According to ch-aviation, the airline operates the following aircraft.
Aircraft Type
Total Aircraft
Airbus A320-200
62
Airbus A320-200N
91
Airbus A321-200
29
Airbus A321-200NX
32
Spirit Airlines operates as an ultra-low-cost carrier, meaning the airline charges for amenities that are often included in the base ticket price of other carriers. According to Cirium, in October 2025 the airline will operate a total of 11,791 flights with a capacity of over 2.2 million passengers.
Frontier Airlines
The airline is conducting over 17,000 flights in October 2025.
Credit: Denver International Airport
Frontier Airlines is another ultra-low-cost carrier that owns a share of the US domestic market. The airline can be traced back to the 1950s, formed as a merger of Arizona Airways, Challenger Airlines, and Monarch Air Lines. However, the airline ceased operations in the early 1980s. A new airline, the current iteration, was founded in 1994.
The Denver, Colorado-based airline operates across the US, flying out of operating bases such as Chicago Midway International Airport, Cleveland Hopkins International Airport (CLE), Harry Reid International Airport (LAS), and Orlando International Airport (MCO), among others. According to ch-aviation, the airline operates a fleet of around 167 aircraft, all of which are narrowbody aircraft. Frontier Airlines currently flies the following aircraft:
Aircraft Type
Total Aircraft
Airbus A320-200
6
Airbus A320-200N
82
Airbus A321-200
21
Airbus A321-200NX
58
Because Frontier Airlines is an ultra-low-cost carrier, it operates an interesting business model that charges passengers for additional amenities and services, such as baggage allowance or advanced seat reservation. Even so, the airline will fly over 17,000 flights in October 2025. According to Cirium, these flights can accommodate over 3.5 million passengers.
JetBlue Airways
JetBlue will fly just under 20,000 total flights in October 2025.
Credit: Shutterstock
JetBlue Airways is another popular domestic carrier that carries a large share of the US market. The airline was founded in the late 1990s, originally as NewAir. Since then, the New York City, New York-based airline has grown as a low-cost point-to-point carrier. The airline flies both domestic and international flights, especially from its main hub at John F. Kennedy International Airport (JFK) in New York.
Originally, JetBlue focused on utilizing only narrowbody Airbus A320 aircraft, similar to how Southwest only operates the Boeing 737 series. However, according to ch-aviation, the airline now flies the following aircraft:
Aircraft Type
Total Aircraft
Airbus A220-300
55
Airbus A320-200
130
Airbus A321-200
63
Airbus A321-200NX
28
Airbus A321-200NX(LR)
11
Embraer ERJ-190
25
JetBlue operates as a full-service airline, with a business class cabin. The airline has grown in popularity among travelers on the East Coast, leading JetBlue to fly just under 20,000 total flights in October 2025. According to Cirium, these flights can accommodate over 3.1 million passengers.
Alaska Airlines
The airline will fly just under 35,000 total flights in October 2025.
Credit: Vincenzo Pace
Alaska Airlines is another popular domestic carrier. The fifth-largest airline in the US can be traced back to the early 1940s. Since then, Alaska Airlines has grown to serve destinations across the US, including from its main hub at Seattle-Tacoma International Airport (SEA).
The airline operates a fleet of only narrowbody aircraft, primarily from the Boeing 737 series. Alaska Airlines also has significant orders to expand its fleet, with open orders for the Boeing 737 MAX 8 and 737 MAX 10. According to ch-aviation, the airline operates the following fleet:
Aircraft Type
Total Aircraft
Boeing 737-700
14
Boeing 737-800
61
Boeing 737-900ER
79
Boeing 737 MAX 8
10
Boeing 737 MAX 9
80
Currently, the airline flies to over 100 destinations in the US, Mexico, Canada, and the Caribbean, although it primarily focuses on connecting cities along the West Coast. According to Cirium, the airline will conduct a total of 34,574 flights in October 2025 with the capacity of just under 4.5 million passengers.
Southwest Airlines
The airline will conduct over 113,000 total flights in October 2025.
Credit: Lukas Souza
The fourth-largest airline in the US is Southwest Airlines. The airline was first founded in the 1960s to connect cities across Texas. Nowadays, Southwest Airlines is based at Dallas Love Field (DAL), although it operates bases at Chicago Midway International Airport (MDW), Houston Hobby Airport (HOU), Denver International Airport (DEN), and Nashville International Airport (BNA), among others.
Southwest Airlines is known for operating only a single aircraft type, all of which are in the Boeing 737 family. Currently, the airline flies over 800 aircraft. According to ch-aviation, Southwest Airlines flies the following aircraft:
Aircraft Type
Total Aircraft
Boeing 737-700
326
Boeing 737-800
203
Boeing 737 MAX 8
289
Over the years, the low-cost carrier has grown to serve over 100 destinations in 42 states, alongside several destinations in Mexico and the Caribbean. According to Cirium, the airline will operate 113,885 total flights in October 2025. These flights will have over 18 million available seats.
United Airlines
The airline will fly over 122,000 flights in October 2025.
Credit: Denver International Airport
Another airline that dominates in the domestic market is United Airlines. The Chicago, Illinois-based carrier is the oldest commercial airline in the US and has grown to rank among the largest airlines in the world since it was founded. Overall, the airline operates an extensive network of domestic and international destinations.
Since the airline operates to such a significant number of destinations around the world, United Airlines flies both narrowbody and widebody aircraft. According to ch-aviation, the airline operates the following aircraft:
Aircraft Type
Total Aircraft
Airbus A319 series
79
Airbus A320 series
71
Airbus A321 series
50
Boeing 737 NG series
329
Boeing 737 MAX series
236
Boeing 757 series
61
Boeing 767 series
53
Boeing 777 series
96
Boeing 787 series
80
United Airlines operates its main base at Chicago O’Hare International Airport (ORD), although it operates significant hubs at Denver International Airport (DEN), George Bush Intercontinental Airport (IAH), Newark Liberty Airport (EWR), San Francisco International Airport (SFO), and Dulles Airport (IAD), among others. In October 2025, according to Cirium, the airline will conduct 122,554 total flights, with capacity for over 14.7 million passengers.
Delta Air Lines
The airline will operate over 132,000 total flights in 2025.
Credit: Shutterstock
The airline conducting the second-most flights in October 2025 is Delta Air Lines. This major carrier was founded nearly 100 years ago and has since grown to conduct over 5,000 daily flights to over 300 destinations across the world. The airline also flies to over 50 countries on six different continents.
Because of the airline’s extensive route network, Delta Air Lines operates a large fleet of over 1,000 aircraft, including both narrowbody and widebody variants. According to ch-aviation, the airline operates the following fleet:
Aircraft Type
Total Aircraft
Airbus A220 series
80
Airbus A319 series
57
Airbus A320 series
48
Airbus A321 series
211
Airbus A330 series
70
Airbus A350-900
38
Boeing 717
80
Boeing 737 NG series
240
Boeing 757 series
110
Boeing 767 series
60
Delta Air Lines has grown to become one of the world’s largest airlines in terms of passengers carried and total flights. According to Cirium, the airline will conduct over 132,000 flights in October this year, with a capacity of over 17 million passengers.
American Airlines
The airline will fly over 160,000 total flights in October 2025.
Credit: Shutterstock
In October 2025, the airline conducting the most domestic flights is American Airlines. The Dallas-Fort Worth, Texas-based airline was founded nearly 100 years ago. Currently, the airline flies to more destinations than any other airline, especially with help from its regional brand, American Eagle.
Since the airline operates such an extensive route network, American Airlines operates a fleet of just over 1,000 total aircraft. According to ch-aviation, American Airlines operates the following fleet:
Aircraft Type
Total Aircraft
Airbus A319 series
132
Airbus A320 series
48
Airbus A321 series
305
Boeing 737 MAX 8
81
Boeing 737-800
303
Boeing 777 series
67
Boeing 787 series
67
American Airlines will conduct over 162,000 flights this month. According to Cirium, these flights will have the capacity of a staggering 19 million passengers, making it the airline operating the most flights in the US.
