United followed suit later in the day, posting reduced fares on some flights from Minneapolis to seven of its hub cities including New York, Chicago and Los Angeles for travel starting April 18. Bargain hunters will see more basic-economy options when searching one-way flights, rather than round trips, because American will not allow flyers to buy a round trip that combines the new cheaper fare on one leg with a regular economy fare on the other. Basic economy fares were introduced by Delta Air Lines several years ago in response to growing competition from discounter Spirit Airlines. The new discount fares could help the big airlines by stimulating new demand and because some people who intend to buy a rock-bottom fare will pick a traditional economy ticket instead, Mann said.