Southwest Airlines has delayed a number of Boeing 737 MAX 7 orders but substantially increased its orders for larger B737 MAX 8s through 2019 and 2020.

The large US regional carrier said it was increasing its fleet investment to support future growth opportunities and modernise its all-Boeing 737 fleet “at favourable economics”.

A total of 40 MAX 8 options were converted to 15 firm orders in 2019 and 25 firm orders in 2020, a deal valued at approximately US$4.5 billion at list price. A total of 23 MAX 7 firm orders from 2019 through 2021 were deferred, however, with 12 now firm orders for 2023 and 11 firm orders for 2024.

Southwest added that it’s 2018 available seat mile growth plans remain unchanged.

The larger MAX 8s can take up to 189 seats compared to the MAX 7’s 172, although Southwest debuted the MAX 8 last year in a 175-seat configuration. It has previously also said it will fly the MAX 7 with 143 passengers.