United Express

Major airlines in the United States had long maintained relationships with regional carriers which fed passengers from small markets to larger cities. The Airline Deregulation Act of 1978 spurred industry consolidation, and as the hub system became more pronounced, airlines formalized these relationships through code sharing, co-branding and listing regional partners' flights in computer reservations systems.

On May 1, 1985, United formally partnered with Air Wisconsin, Horizon Air, and WestAir as United Express, feeding its hubs at Chicago–O'Hare, Seattle/Tacoma, and San Francisco, respectively. Aspen Airways joined in 1986 the hub at Denver–Stapleton. Horizon Air was bought by Alaska Airlines in 1987 at which time Horizon's contract with United was cancelled and a new carrier, North Pacific Airlines (NPA), was established by WestAir to service the Seattle hub as well as hubs at Portland, Spokane, and Boise. Aspen was dismantled in 1990 being sold to Air Wisconsin and Mesa Airlines. NPA was merged into its parent, WestAir, in 1991. San Juan Airlines of Seattle and SouthCentral Air of Anchorage, Alaska, also operated as United Express from 1987 through 1989.

In 1988, Presidential Airways became a United Express carrier for United's new hub at Washington–Dulles, but quickly floundered. In response, WestAir formed an eastern division to serve Dulles. WestAir itself experienced turmoil; in 1991 it spun off the new division into an independent company, Atlantic Coast Airlines (ACA), which years later would go on to become Independence Air.

In 1990, Mesa Airlines took over all of the United Express routes from Denver formerly operated by Aspen Airways except the Denver to Aspen route which went to Air Wisconsin. Mesa also added a number of new routes from Denver as well. In 1992 Mesa created a new division called California Pacific Airlines to begin new United Express service from the Los Angeles hub. In 1995, Mesa took over all United Express routes at the Seattle and Portland hubs formerly operated by WestAir. Mesa Airlines contract operating as United Express was cancelled in 1998 at which time Air Wisconsin and Great Lakes Airlines took over the Denver routes while SkyWest took over the Los Angeles, Seattle, and Portland routes.

In 1992, Great Lakes Airlines became a United Express partner, followed by Trans States Airlines the following year. In 1997, as United officially designated Los Angeles one of its hubs, SkyWest Airlines became a United Express partner as well. Great Lakes left the United Express system in early 2002, although it continued to do codeshare flights until they ceased operations in 2018.

In 1993, Trans States Airlines started United Feeder Service (UFS), to operate British Aerospace BAe ATP aircraft for United Airlines. The aircraft, originally owned by Air Wisconsin, were transferred and subsequently owned by United. UFS operated routes to Chicago–O'Hare from close markets in the U.S. Upper Midwest. UFS was eliminated from the United Express carrier network in 1999 and disappeared.

When United declared for Chapter 11 reorganization in 2002, it pressured its regional partners for reduced fees. In 2004, ACA canceled its contract and attempted to reinvent itself as low-cost carrier called Independence Air, but ceased operations only 18 months later. The next year, Air Wisconsin unsuccessfully bid to retain its flying contract, though it did retain some ground-handling United Express operations. To compensate, United initiated new service agreements with Colgan Air, Trans States subsidiary GoJet Airlines, and Republic Airways Holdings subsidiaries Chautauqua Airlines and Shuttle America. Mesa Airlines was also reinstated into the United Express system.

In 2005, United announced that service levels on major United Express routes would be upgraded to a new product called explus. Routes with explus service offer First Class seats and meal service on larger, 70-seat Embraer 170s and 66-seat Bombardier CRJ700s. Expanding the traditional regional partner role, United started to use the airplanes configured with explus amenities instead of, or alongside with, mainline jets on routes linking large cities, such as Chicago to Houston.

United announced a new Express focus city in San Antonio in 2006, but the experiment was short-lived. Trans States was the carrier operating the San Antonio operation.

United decided to cancel Dash 8 and CRJ200 service with Mesa Airlines in November 2009. On November 16, 2009, it was announced that ExpressJet would begin operating Embraer ERJ 145s beginning in the spring of 2010. Mesa Airlines continued service using CRJ700 regional jets and added the Embraer 175 in 2015.

All Continental Express and Continental Connection service officially merged into United Express in late 2010, including that of Cape Air, which was operating as Continental Connection on behalf of Continental Micronesia in Guam. Silver Airways was also a Continental Connection carrier that converted to United Express using turbo prop aircraft. Silver operated throughout Florida, as well as routes from Washington Dulles Airport; however, their affiliation as United Express ended in 2013.