In the past decade, many airlines have significantly improved business and first class offerings — particularly on long-haul international flights. From United Airlines to Qatar Airways, several airlines introduced excellent new business class seats that fully recline into lie-flat beds. Best of all, you can sometimes fly in these business class lie-flat seats on flights within the U.S.

However, there are plenty of pitfalls when seeking out lie-flat business class seats. To avoid disappointment, you'll need to know what you're looking for to find these premium seats. Let's dig into which airlines have lie-flat seats in business class and how you can book them.

Which airlines have lie-flat seats in business class

As a general rule, most airlines install business class lie-flat seats on larger, twin-aisle aircraft — such as Airbus A330, A350 and A380, and Boeing 767, 777 and 787 Dreamliner aircraft. You can use a tool like ITA Matrix to specifically seek out these types of aircraft for the best chance of getting a lie-flat business class seat.

This is especially true on aircraft that operate long-haul flights from the U.S. to Europe, Asia, Australia, New Zealand and southern South America. However, as you'll see below, not all wide-body aircraft have lie-flat seats when flying within other regions of the world.

Although the quality of the seat varies between aircraft, you can be sure that you're getting a lie-flat seat in business class on the following U.S. airlines and aircraft types:

American Airlines: Boeing 777 and 787 aircraft.

Delta Air Lines: Airbus A330 and A350 and Boeing 767 aircraft.

United Airlines: Boeing 767, 777 and 787 aircraft.

JetBlue Airways: A321 aircraft with JetBlue Mint.

Meanwhile, avoid flying Alaska Airlines, Southwest Airlines, Frontier Airlines, Spirit Airlines and most other low-cost airlines if you want to book a lie-flat business class seat.

Airlines that don't have lie-flat seats in business class on wide-body aircraft

Most airlines have lie-flat seats in business class on wide-body (twin-aisle) aircraft. However, watch out for some notable exceptions to this general rule.

For example, some Asia-based carriers opt to configure some of their larger aircraft for domestic and regional routes. On these aircraft, business class may only have reclining seats — similar to what you'll find in domestic first class within the U.S. — rather than lie-flat seats.

Specifically, Japan Airlines uses recliner business class seats on Airbus A350, Boeing 787 Dreamliner and Boeing 767 aircraft that are configured for domestic flights. Similarly, fellow Japanese airline All Nippon Airways, also known as ANA Airlines, uses recliner business class seats on select 777, 787-8 and 787-9 Dreamliner aircraft.

(Photo courtesy of Japan Airlines)

Other times, airlines have installed angle-flat seats in business class rather than truly lie-flat seats. For example, Emirates operates the largest Boeing 777 fleet, with a whopping 153 Emirates 777 aircraft in its fleet at the time of writing. Unfortunately, even on an airline as prestigious as Emirates, not all of its business class seats recline into fully lie-flat beds.

Instead, seats recline into an angle-flat bed. Some travelers won't find the angle-flat bed an issue. However, if you need to lie completely flat to sleep well, watch out for these angle-flat seats.

Airlines that offer lie-flat seats on smaller aircraft

In addition to wide-body aircraft, some airlines opted to install lie-flat business class seats on select smaller aircraft.

For example, American Airlines utilizes specially configured "A321T" aircraft on premium coast-to-coast routes, such as New York City to Los Angeles and San Francisco. On these aircraft, American Airlines has 10 first class seats — arranged with just one seat on either side of the aisle — and 20 business class lie-flat seats.

(Photo courtesy of American Airlines)

Similarly, United utilizes aircraft with lie-flat business class seats on coast-to-coast flights between Newark/New York and Los Angeles/San Francisco and between Boston and San Francisco. United operates these flights either using aircraft with lie-flat United Polaris business class seats or single-aisle Boeing 757 aircraft with lie-flat seats.

JetBlue is another example of an airline that uses lie-flat business class seats on single-aisle aircraft. JetBlue Mint is only found on select Airbus A321 aircraft. Although there are two different types of Mint class seats, both recline into fully lie-flat beds.

And it's not just U.S.-based airlines that have lie-flat business class seats on single-aisle aircraft. For example, Copa Airlines' new Boeing 737 MAX aircraft uses lie-flat business class seats just like you'll find on American Airlines A321T and United Boeing 757 aircraft. This Copa 737 lie-flat business class seat product initially launched with routes between a few Latin American cities and Los Angeles.

How to find business class lie-flat seats on domestic flights

Airlines typically utilize their premium aircraft with lie-flat business class seats on long-haul international flights. However, you can occasionally find these aircraft with lie-flat business class seats operating on domestic flights.

Airlines sometimes will fly these aircraft between hubs to maximize their usage. Other times, premium cabin demand is high enough that airlines will intentionally schedule these premium aircraft on certain routes — such as an American Airlines' flight between Miami and Los Angeles.

One resource that's excellent for finding these types of flights is a website called Where the Widebodies Are. Just enter a departure airport, airline and/or departure date. Then select "submit" to get a list of the routes with wide-body aircraft operating at least some flights.

If you enter a specific date, the website will return a list of the flight numbers, routes, and departure and arrival times, as well as an abbreviated code for the type of aircraft being used. The website even generates a map to make it easier to visualize the routes.

How to confirm if a flight has business class lie-flat seats

The easiest way to confirm whether or not an aircraft has lie-flat business class seats is to use a tool like Google Flights or SeatGuru.

Google Flights will show details such as seat pitch, Wi-Fi availability, power availability and more in the flight details for each flight. Just select the down arrow on a particular flight result to see all of these details. Business class seats that lie flat will be labeled with a "lie flat seat" designation.

SeatGuru can also be a great resource for travelers looking for an easy way to check the details of a flight. Say you're booked to fly an American Airlines A321 aircraft and want to confirm whether it has lie-flat business class seats. From SeatGuru’s homepage, enter the airline, date and flight number for the flight you want to check. Then, select "find" to search.

The results will show the flight’s departure and arrival times, aircraft type and amenities. However, to see the seat map, you'll need to select the "View map" button.

In this case, SeatGuru opens the seat map for "Airbus A321 (32B) Layout 3" — commonly known as the "A321T" configuration — with lie-flat seats in Flagship First and Flagship Business.

If you're looking to book business class lie-flat seats

Most airlines opt to install lie-flat business class seats on twin-aisle wide-body aircraft — particularly those operating long-haul international flights. However, you can luck into booking these premium business class seats on certain domestic routes. Just look for flights using wide-body aircraft or those on premium coast-to-coast routes, such as New York to Los Angeles.

Before you splurge for business class, though, make sure to use a tool such as Google Flights or SeatGuru to make sure that the aircraft you're booking has lie-flat seats in business class.