Thames Transit was a bus and coach company which operated in the Oxford area. As well as running a number of local services, it also ran a regular service to London (via the M40 motorway) under the Oxford Tube brand. It was sold in July 1997 to Stagecoach, and traded as Stagecoach in Oxfordshire. As of 2022 it is part of Stagecoach West.

Thames Transit was founded in March 1987 by Harry Blundred, a former bus driver and controller, who led a management buyout of Devon General during the privatisation of the National Bus Company in August 1986. Blundred started Thames Transit from scratch in Oxfordshire with buses cascaded from his Devon General operation on two routes:

The firm struggled under intense competition from the incumbent City of Oxford Motor Services, but ultimately succeeded in increasing patronage through a series of innovative approaches. Among these, the use of branding was particularly successful in the case of the Oxford Tube and Blackbird Flyer. Later branding efforts were not always so successful, and Oxford Tube is the only brand name to survive today.

Competition remained fierce and in the mid-1990s a price war erupted, with for example a 12-journey ticket between Oxford and London costing just £15. The price war was abandoned before these unsustainable fares could drive either company out of business.

The firm is noted for introducing minibuses to Oxford. The original vehicles on local routes were sixteen seater Ford Transits, colloquially called Snoopys for their resemblance at the front to the cartoon character. The buses featured a single front entrance and exit door and room for four standing passengers. They eased initial recruitment concerns because drivers did not have to hold a full PSV licence to drive them. The primary reason behind their use, however, was that Blundred felt greater profitability could be gained through running small buses at a high frequency, rather than running larger buses half-empty at a low frequency.

In 1989 Thames Transit expanded by buying South Midland, the former country area of The City of Oxford Motor Services, primarily operating rural routes in Oxfordshire. This acquisition strengthened Thames Transit's hand against City of Oxford Motor Services, providing it with several routes where it was the sole provider.

The company then grew significantly in the early 1990s, introducing larger Mercedes-Benz minibuses with 32-seat capacity and buying new vehicles for the Oxford Tube coach service, which was starting to perform well against rival City of Oxford's Citylink service. City of Oxford itself had been forced to spread its defensive tactics following the South Midland acquisition, and this allowed Thames Transit to grow.

In 1994 the firm bought its first midibuses: a fleet of 9.8 metre step-entrance Dennis Darts. Thirteen were bought for the original number 1 route, and new branding was applied, adorning the buses with a giant blackbird called 'Bertie' and the service named 'The Blackbird Flyer'. Continuing the minibus philosophy, the buses were scheduled every four or five minutes. There was a noticeable shift of traffic away from City of Oxford as passengers responded to Thames Transit's new branding and vehicles.