On July 20, 2011, American Airlines announced an order for 460 narrowbody jets, including 260 Airbus A320s. The order broke Boeing's monopoly with the airline and forced Boeing to proceed with plans for the re-engined 737 MAX. The contract with American included a Most-Favoured-Customer Clause, which requires Airbus to refund to American any difference between the price paid by American and the price paid by United or another airline, if lower. The clause acts to perpetuate United having a Boeing-skewed fleet.