Chiltern Railways has apologised to passengers who were stranded on a train just outside Bicester for more than three hours on Monday.
The 7.30pm train from London Marylebone to Birmingham Snow Hill experienced problems with its safety systems as it approached Bicester just after 8.30pm.
Because of this, the train did not reach Bicester North station until 11.45pm.
A spokesman for Chiltern Railways said: "While delays of this length are unusual on our service, we do consider them to be completely unacceptable."
Severe delays were experienced by passengers on other trains, as a backlog was created.
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