A blunder by Oxford station staff left dozens of passengers locked out and unable to catch their train.
People were left waiting until 08:00 BST - 15 minutes after the first train to London had departed.
Commuter Robert Atkins said on Twitter: "How is Oxford station still not open? The first train has already left but all doors closed."
Great Western Railway (GWR) apologised and said "staff arrived later than they should have".
Francis Barr, from Oxford University, said: "My partner was on her way to London for work first thing this morning.
"She had a ticket booked for the 07:43 Chiltern Railways train to Marylebone but was unable to get into the station since it was still locked and there were no staff to be seen."
"There were over 50 people waiting, more by the time the doors were opened," he added.
Mr Atkins tweeted that the person who called customer services was told "the only person with keys had decided to not come in".
A GWR spokesman said: "We're sorry staff arrived later than they should have, and this incident is being looked into."