Problems on rail lines at Didcot have been fixed, according to Network Rail.
A points and track circuit failure occurred at 11.41am.
Network Rail spokesman Nathan Quigley said: "A reduced service continued to run between Reading and Oxford, and Reading and Bristol, but trains were subject to some delays.
"The fault was corrected by 1.30pm and services are presently recovering."
A fatality at Taplow in Buckinghamshire earlier today also affected services in Oxfordshire.
A man is believed to have stepped in front of the 5.35am Plymouth to Paddington train at 9am.
Mr Quigley said: "All services were immediately suspended while engineers and emergency services attended the scene to investigate.
"British Transport Police confirmed the incident as a non-suspicious fatality.
"At 9.35am relief lines opened, with a reduced service operating and some delays.
"The incident caused a major disruption."
Main lines reopened at 11am.
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