Northwest Airlines and Midwest Airlines have signed an agreement to form a codeshare partnership. This agreement formalizes a Memorandum of Understanding the two carriers signed in May. Passengers will be able to book a trip that includes both airlines under a single ticket with all segments earning miles in either airlines’ frequent flyer program. The agreement will add 250 city pairs and more than 1,000 new flight options for customers of both carriers. The program will be phased in by market, with the initial destinations to include Midwest flights between Milwaukee, Kansas City and Omaha to major cities on the West Coast. You can purchase codeshare tickets now for travel Nov. 17, 2007 and beyond. The two airlines have had a reciprocal frequent flyer partnership since May 2006 and recently Midwest was acquired by private equity firm TPG, backed in part by Northwest Airlines.