Some airlines may designate an entire economy class as premium, such as United p.s. on its transcontinental Boeing 757-200 premium service aircraft. In other airlines premium economy may be what used to be regular economy before more seats were added, or just the most attractive rows in the economy section. Premium Economy tickets also normally earn more mileage in an airline's frequent flyer program, attracting a bonus between Economy and Business.[citation needed] These upgrades tend to be more common on wide-body aircraft, such as the Boeing 747 and 777, and less common on narrow-body aircraft, such as the Boeing 737.