Due to engineering work between Oxford and Didcot Parkway, Cotswold Line trains will only operate west of Oxford on Sunday, March 26.
Replacement buses will link Oxford and Didcot, to connect with trains to and from Reading, Slough and London Paddington.
Most Cotswold Line trains will operate between Oxford, Worcester and Great Malvern, with a number extended to and from Hereford.
In addition, the 19.20 from London Paddington to Hereford and the 20.50 from Paddington to Worcester Shrub Hill will both run via Swindon, calling en route at Didcot to connect with buses to Oxford.
Click here to visit the GWR website journey planner for details of services on the day.