The changes will start to come into effect next month when new timetables are launched around Banbury.
New buses will be delivered for the Banbury-Oxford and Banbury-Brackley routes later this year.
From Sunday, September 4, the 59/59A/59B services between Oxford and Banbury are to be renumbered as S4, joining the group of S-series services linking the city with the west and north of the county.
The existing timetable will remain in force with some minor changes. The early morning bus into Oxford via Lower Heyford and Bletchingdon will instead run via Tackley.
Chris Child, marketing manger for Stagecoach Oxfordshire, said: “S-series was launched in 2009 when routes to Bicester, Witney, Carterton, Chipping Norton and Charlbury were upgraded.
“It’s about highlighting how easy it is to get around by bus. The new buses will be fitted with Euro 5 engines, providing outstanding environmental performance. They will have easy access entrances, making it simple to get on and off with shopping, a wheelchair or buggy.
“They include CCTV for added security and peace of mind, and will be added to the Oxford real-time information system, so you can text and find out when the bus is due.”
Stagecoach will also take over long-term operation of the Banbury-Woodford Halse-Daventry service, which it stepped in to run at short notice after former operator Geoff Amos Coaches went out of business at the start of this month.
The existing GA01 service will be replaced by route 200 next month.
Ken Atack, Cherwell district councillor for Cropredy ward, had feared for the future of the route, which serves the Bourtons, Cropredy, Williamscot, Wardington and Chipping Warden.
He said: “This is really good news. We were very keen to see a long-term replacement service.
“I’d expected a longer experimental period for Stagecoach to assure themselves the service was viable.”
Other changes from September 4 will see the B1 and B2 routes in Banbury retimed to improve reliability at busy periods on weekdays and buses on route B8 retimed to leave stops in Sinclair Avenue and Austin Drive two minutes earlier than they do now, with the first Sunday service running at 9am instead of 9.30am.
A larger bus will be used on the 7.25am No 488 service from Chipping Norton to Banbury to cope with passenger numbers.
After consultation with passengers, the 500 service between Banbury and Brackley will enjoy extra services from Mondays to Saturdays, running every 20 minutes instead of half-hourly.