A total of 4,887 737NG aircraft has been delivered by the end of April 2014, with more than 6,700 ordered. Currently, only the -700, -800, and -900ER are produced, as the -600 was not popular, and neither was the -900. Its primary competition is with the Airbus A320 family. Upgraded and re-engined models in development as the 737 MAX series will eventually supplant the 737NG.