RELATED: American Airlines Is Getting Rid of This on Flights, Effective Immediately. Noting that searches for “flexible airlines’’ have increased by 733% in the last 12 months, the online search tool Next Vacay analyzed domestic airline policies surrounding flexibility and determined the two least flexible among them: Allegiant Air and Alaska Airlines. The findings came from data points including change fees, restrictions to cancel flights, travel insurance, and refund options. These metrics were assigned scores, which the researchers then added together to come up with rankings. RELATED: This Is the Worst Airline in the U.S., New Data Shows. Unlike many other airlines’ new no-fee policies in response to the pandemic, Allegiant charges $25 per person, per flight segment to change a booking. And if you need to cancel more than 24 hours after booking, you will be charged a fee of $75 per passenger, per segment. Next Vacay notes that Allegiant does offer Trip Flex, which allows passengers to change an itinerary once or even postpone the whole trip without paying the change fees. So if you fly this airline, consider purchasing insurance. RELATED: Delta CEO Just Warned This Major Change Is Coming to Flying. Alaska Airlines offers no change fees on its main and first-class fares — but not without plenty of restrictions. The airline only allows you to change your flight once before it charges a fee, and it charges a fee of $25 to $50 for same-day changes. Plus, in order to cancel your ticket online and receive a refund or credit, your purchased reservation must meet a range of criteria, including being ticketed using U.S. dollars and being independent from a group booking.ae0fcc31ae342fd3a1346ebb1f342fcb The research also noted the most flexible airlines to fly, which include American, Southwest, Delta, and United. Southwest Airlines has long been known (and loved) for its flexibility—well before the pandemic—offering no change fees and refundable Anytime and Business Select fares. And if you have to cancel, just do so more than 10 minutes before your flight’s scheduled departure time for a refund in the form of travel credit. And consider that American not only charges no change fees for any domestic, short-haul, and some long-haul international flights, but it also allows travelers to purchase fully refundable tickets. Book your cabin mindfully, though: Even on American, basic economy flight tickets remain non-refundable and non-changeable for travelers. RELATED: For more up-to-date information, sign up for our daily newsletter. “Whether it’s across the globe or closer to home, many passengers are becoming more cautious about the reliability of flights as the travel industry attempts to get back to normal,” Next Vacay founder and C.E.O. Naveen Dittakavi, said in a release. “There are many different factors to consider when booking a flight including change fees, refund options, canceling the flight, and travel insurance. Each airline has different specifications so make sure you do your research before booking your ticket to find the best option for the flexibility you’re looking for.” RELATED: Never Forget to Do This Before Boarding, Flight Attendant Warns.