Mesa Air Group Inc. said Friday that United Airlines did not extend an agreement under which Mesa operated 26 regional jets for the larger carrier.

Mesa operates the CRJ-200 aircraft under a code-sharing agreement with United. Mesa said the deadline for extending the deal had passed, and it expects to exit from the service by the end of April 2010.

According to Mesa's Web site, it currently operates 58 regional jets and 10 turboprop planes for United under the United Express brand.

Mesa also operates planes for other regional operations of major carriers, including Delta Connection and US Airways Express.

Regional jets are smaller than the aircraft that big airlines use on most routes. They are often used to ferry travelers to hub airports, where they can connect with other flights.