Southwest Airlines is arguably Boeing’s most important customer, as the airline has purchased over 1,700 737s. June 2026, in fact, marks the 50th anniversary of when Southwest first ordered new 737s from Boeing, as the 737s that it purchased beforehand were non-taken units originally ordered by other airlines. While Southwest did briefly operate leased Boeing 727s, the carrier has otherwise been all-in on the 737, and has even committed to operating an all-737 MAX fleet by 2031.

However, strikingly, as larger narrowbodies have become as popular as ever, Southwest has focused on the 737 MAX 8 and 737 MAX 7, the two smallest variants of the 737 MAX family. Southwest has not ordered the 737 MAX 9 or MAX 10, and there’s no indication that the carrier is interested in these two variants. This is especially notable considering that the 737 MAX 10 has become increasingly popular worldwide, even being ordered by other all-737 operators like Ryanair. Southwest is the most notable hold-out.

Why Large Narrowbodies Are So Popular Today

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When designing an aircraft, manufacturers typically start with a baseline design, which can then either be stretched or shrunken. Stretching a plane lowers per-seat costs, but worsens capability, while the opposite is true for a shrink. Manufacturers may also alter the design, such as by strengthening the structure on a stretch, to minimize the downsides of altering the design, but this also reduces the benefits.

With the prior-generation Boeing 737, the baseline 737-700 was outsold by the improved and stretched 737-800, while the shrunken 737-600 and the stretched 737-900/737-900ER were duds. With the 737 MAX, however, all models have gained range on account of their more fuel-efficient engines, which means that even the stretched 737 MAX 10 is capable enough for most airlines’ needs.

In addition, the plane burns only marginally more fuel than the 737 MAX 8, resulting in lower per-seat costs given the large capacity increase. As such, the 737 MAX 10 has become the second-most popular 737 MAX model, while the competing Airbus A321neo has outsold the entire 737 MAX family on its own. The capabilities offered by the smaller variants are no longer needed.

What’s more, the CFM LEAP engines on the 737 MAX are heavier than the CFM56 models used on the 737NG. This resulted in a larger weight gain proportional to the aircraft’s weight, hampering the economics of the 737 MAX 7. The 737 MAX 7 is longer than the 737-700, partially improving economics, but the competing Airbus A319neo is identical to the A319-100 apart from the engines and consequently, has only received 57 sales.

Why Southwest Wants Smaller Planes

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Southwest has traditionally avoided the largest variants of the 737 family. It never flew the 737-400, instead favoring the 737-300 and 737-500, while it waited until 2012 to begin flying the 737-800, with 175 seats. Up to that point, Southwest only flew the 737-700 with 143 seats (now reconfigured with 137 seats), the 737-300 with 137 seats (retired in 2017), and the 737-500 with 122 seats (retired in 2016), while it retired the 122-seat 737-200 in 2005.

Southwest Airlines’ business model has traditionally centered around point-to-point routes served with a huge number of daily frequencies. This appeals to business travelers, while Southwest’s diverse route network helps it capture huge swaths of market share. Southwest ultimately operates as a hybrid between a legacy carrier and a budget airline, as budget airlines focus on connecting underserved cities to popular vacation destinations with limited daily frequencies and focus heavily on per-seat costs.

Southwest primarily ordered the 737-800 due to existing airport capacity limitations, but the 737-700 has remained the dominant aircraft type within its fleet. What’s more, the carrier is highly focused on maximizing fleet commonality, currently operating just three aircraft variants and looking to standardize on just two. While a 737 MAX 10 order could come in the future, the carrier currently requires small planes and as few variants as possible, reflected in its order book consisting of 737 MAX 7s and 737 MAX 8s.

Southwest’s Relationship With The 737 MAX 7

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Whereas the 737 MAX 8 and MAX 9 are essentially tweaked versions of the 737-800 and 737-900ER with the CFM LEAP, the 737 MAX 7 is quite different from the 737-700. Essentially, Boeing redesigned the aircraft to retain the structure of the 737 MAX 8, making it a straight shrink, and the plane is also larger than the 737-700. As a whole, the 737 MAX 7 only burns marginally less fuel than the MAX 8, while offering less revenue potential, which is why it’s only received around 300 orders.

However, Southwest holds 269 of these orders, and the changes to the 737 MAX 7 were requested by the Dallas-based carrier, which wanted the aircraft to have lower per-seat costs. While the carrier also ordered a total of 496 737 MAX 8s, the MAX 7 will be an integral part of its fleet. With this, there’s little need for a 737 MAX 10 order, since the carrier will be upgauging network-wide through the widespread use of the 175-seat 737 MAX 8 and the 737 MAX 7, with its increased capacity over the 737-700.

Southwest has taken over 300 of its 737 MAX 8s, and is now waiting for the 737 MAX 7 to be certified. Currently, it’s anticipated that the MAX 7 will be certified by the end of the summer, while the 737 MAX 10 will be done by year’s end. This is big news for Southwest as well as the dozens of customers who have ordered the MAX 10. These planes have been delayed for nearly six years, and for Southwest, it will allow the airline to accelerate the retirement of its 737NG fleet.

The Market Position Of The 737 MAX Family

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The 737 MAX 8 is the most popular variant of the 737 MAX family, as it’s received over 4,800 orders, amounting to around 70% of all 737 MAX orders. It’s outsold the competing A320neo, largely because it can seat slightly more passengers and has slightly more range. The 737 MAX 9, on the other hand, has not been competitive against the A321neo, as it simply costs more to operate per seat despite having lower trip fuel burn.

This exact same dynamic occurred between the A321-200 and the 737-900ER. The Airbus A321neo is larger, more economical, and fairly capable even in its most basic form. As such, it’s been a runaway success, and having received about 64% of all A320neo family orders, it is one of the most-ordered commercial aircraft variants of all time.

This is why the 737 MAX 10 is so important, as it promises to deliver per-seat costs that are competitive with the A321neo. It’s received over 1,400 orders already, and once the MAX 10 finally enters service, the 737 MAX 9 will become largely irrelevant. The 737 MAX 7 is not selling well, but this isn’t a major issue for Boeing. Like any company, Boeing aims to maximize profits from its aircraft programs.

The 737 MAX 7 is the cheapest aircraft that Boeing sells, meaning that the company earns less revenue from MAX 7s. As a whole, the plane largely exists for Southwest Airlines as well as for any customer that wants it. This is also why Airbus isn’t concerned about its A319neo only selling 57 units. It’s available for those who want it, but Airbus would rather sell A321neos otherwise.

Southwest’s Continued Focus On The 737

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Southwest is one of the world’s largest airlines, with nearly 800 planes, and all of them are 737s. While the company has discussed adding another type, most recently focusing on the Airbus A220, it’s always chosen to stick with the 737. By only flying the 737, Southwest can standardize on one set of parts for nearly 800 aircraft, train staff on one type of aircraft, and easily swap aircraft on certain routes with little operational impact.

This focus has allowed Southwest to run an extremely streamlined operation on an unprecedented scale. Southwest even tends to keep its aircraft variant mix simple, since operating multiple sizes of 737 introduces complexity, albeit less so than adding another aircraft type. With Southwest’s aim to standardize on the MAX 7 and MAX 8, a MAX 10 order will only come in the distant future if airport constraints truly necessitate it.

Meanwhile, although the Airbus A220-300 is the market leader in its segment, the 737 MAX 7 was specifically tailored for Southwest, meaning that the A220 never really stood a chance. Eventually, Southwest will need to add a new aircraft type when the Boeing 737 is finally sunsetted.

However, for now, the airline remains an all-737 operator, and it would be the upset of the century if another manufacturer manages to score a win. Meanwhile, the 737 MAX 10 is largely out of the question for now, as Southwest focuses on two 737 variants with a lower capacity.