Frontier took delivery of its first Airbus aircraft (an A319) in 2001 and simultaneously launched with it DirecTV in-flight television along with a new company livery. Frontier Airlines was the launch customer of the Airbus A318 in 2003. In mid-April 2005, Frontier officially became an all-Airbus fleet, retiring its last Boeing 737.
In May 2017, Allegiant Air took delivery of its first brand-new A320. Allegiant took delivery of ten new A320s in 2017 and is scheduled to accept two in 2018. All new aircraft will be painted in Allegiant's new livery at the time it is delivered. Older Airbus aircraft will be repainted during their C-checks. The new Airbus aircraft will have fuel-efficient sharklets. The new A320s seat 186 passengers, an increase of the 177 seats that are found in the rest of the Allegiant A320 fleet. To fit the additional nine seats, Allegiant opted for the Airbus Space-Flex V2 Lavatory. 
On October 31, 2017, the final 757 was retired from service, leaving Allegiant with only their A320 Family and MD-80 series fleets. In November 2018, the last MD-88s operated by Allegiant were retired, with Allegiant now operating an all-Airbus fleet. The move to the newer all-Airbus fleet has allowed Allegiant to benefit from lower fuel and maintenance costs, as well as operate in some airports which could not be served by the MD-80s.
In August 2017, Allegiant announced a new base would be established at the Indianapolis International Airport. The base began operations in early 2018. In February 2018, Allegiant also announced a new base would be established at the Destin–Fort Walton Beach Airport. In June 2018, Allegiant added another base at McGhee Tyson Airport in Knoxville, Tennessee. In January 2019, Allegiant announced they would be adding another base at Gerald R. Ford International Airport in Grand Rapids, Michigan.
On August 4, 2008, the Associated Press reported that jetBlue would replace their recycled pillows and blankets with an "eco-friendly" pillow and blanket package that passengers would have to purchase for use. Each package will cost $7 and will include a $5 coupon from retailer Bed, Bath and Beyond. This decision is the latest in a series of moves designed to increase revenue. jetBlue told the Associated Press that it expects to collect $40 million from passengers selecting seats with extra legroom and $20 million from passengers paying $15 to check a second bag. As of September 8, 2008 JetBlue charges passengers $10–30 for an extended-leg-room seat depending on the length of the flight.
Animal concepts used in the livery extend into Frontier's marketing as well. Each animal has a specific name. Animal aircraft used in their radio and television commercials include Jack the rabbit, Grizwald the bear, Foxy the fox (for whom Jack has a crush), Flip the dolphin (who always gets stuck going to Chicago rather than the warmer climates the others are going to), Larry the lynx, Hector the sea otter, and Sal the cougar. New additions are Penguins Jim, Joe, Jay, and Gary, a barbershop-style quartet, singing the praises of EarlyReturns to an audience of Frontier's well-known characters from the "a whole different animal" campaign, Hector the otter, advertising Frontier's expanding service to Mexico, and Polly the Parrot, who won the new animal audition in 2012.
Frontier Airlines was incorporated on February 8, 1994, by a group that included executives of the original incarnation of Frontier Airlines in response to the void left by Continental Airlines' 1993 shutdown of its Denver (Stapleton) hub. Scheduled flights began five months later in July 1994 using Boeing 737-200 jetliners on routes between Denver and four destinations in North Dakota: Bismarck, Minot, Fargo and Grand Forks. By January 1995, Frontier had expanded its route network from Denver and was serving Albuquerque, New Mexico; Billings, Montana; Bismarck, N.D.; Bozeman, Montana; El Paso, Texas; Fargo, N.D.; Great Falls, Montana; Las Vegas, Nevada; Missoula, Montana; Omaha, Nebraska; and Tucson, Arizona with 737's. Like the original airline of the same name, the new Frontier operated a hub at Denver (DEN) and for the first nine years used the slogan "The Spirit of the West" which was displayed above the windows and just behind the cursive letters "Frontier" on the fuselage of their aircraft. In 1999, Frontier signed agreements to begin purchasing and leasing Airbus A318 and A319 jet aircraft and had also added Boeing 737-300 jetliners to its fleet as well. Also by September 1999, the airline was serving destinations from coast to coast in the U.S., having expanded its route network to include Atlanta (ATL); Baltimore (BWI); Bloomington/Normal, Illinois (BMI); Boston (BOS); Chicago (MDW, Midway Airport); Dallas/Fort Worth (DFW); Phoenix (PHX); Los Angeles (LAX); Minneapolis/St. Paul (MSP); New York City (LGA, LaGuardia Airport); Orlando (MCO); Portland, Oregon (PDX); Salt Lake City (SLC); San Diego (SAN); San Francisco (SFO); and Seattle (SEA), all served from its Denver hub.
For many years, analysts had predicted that jetBlue's growth rate would become unsustainable. Despite this, the airline continued to add planes and routes to the fleet at a brisk pace. In addition in 2006, the IAM (International Association of Machinists) attempted to unionize JetBlue's "ramp service workers", in a move that was described by JetBlue's COO Dave Barger as "pretty hypocritical", as the IAM opposed jetBlue's creation when it was founded as New Air in 1998. The union organizing petition was dismissed by the National Mediation Board because fewer than 35 percent of eligible employees supported an election.
As Republic Airways Holdings was in the process of bidding to acquire Frontier in 2009, it was also in the process of acquiring Milwaukee-based Midwest Airlines. Through the fall and winter of 2009, Republic operated its two new acquisitions as separate brands. However, to improve efficiency by better matching aircraft capacity to route demand, Republic began to intermix the fleets of the two airlines, swapping a portion of its higher-capacity planes from Frontier with its smaller-capacity planes from Midwest and vice versa. However, the move caused some confusion amongst the public, as the two brands did not offer the same amenities and did not match the amenities mentioned on the airfare. As a result, in the Spring of 2010, Frontier and Midwest Airlines announced that their brands would merge, with Frontier being the surviving brand. This was a merger of brands only—no Midwest Airlines aircraft was ever operated by Frontier, as by this time, all Midwest Airlines flights were operated on its behalf by other Republic Airways Holdings subsidiaries.
On April 10, 2008, Frontier filed for Chapter 11 bankruptcy in reaction to the intent of its credit card processor, First Data, to withhold significant proceeds from ticket sales.[better source needed] First Data decided that it would withhold 100% of the carrier's proceeds from ticket sales beginning May 1. According to Frontier's press release, "This change in practice would have represented a material change to our cash forecasts and business plan. Unchecked, it would have put severe restraints on Frontier's liquidity..." Its operation continued uninterrupted, though, as Chapter 11 bankruptcy protected the corporation's assets and allowed restructuring to ensure long-term viability. After months of losses, Frontier Airlines reported that they made their first profit during the month of November 2008, reporting US$2.9 million in net income for the month.