Police are appealing for information after a robbery at Launton Post Office, near Bicester on Monday.
A man forced his way into the store on Sherwood Close as was being locked up at about 1pm.
He pushed the single female staff member into the back of the building and forced her to empty the till and hand over a substantial amount of cash.
The offender is described as stocky, mixed race, in his late twenties. He is around 5ft 8ins, clean-shaven and was wearing a black hooded top, black thick-rimmed glasses and black trousers or jeans.
The victim was uninjured during the incident and there was nobody else in the shop at the time.
A silver Vauxhall Astra was seen speeding away from the scene at around the time of the robbery.
Investigating officer, detective constable Ian Gibbard, from Force CID, said: “While this was an upsetting experience for the victim, it is fortunate she was unharmed during the incident.
“This type of crime is thankfully rare in Launton, however we would urge anyone with information about this incident to contact police via 101.
“If you don’t want to speak directly to the police you can contact the independent charity Crimestoppers anonymously on 0800 555 111 or online at www.crimestoppers-uk.org. No personal details are taken, information is not traced or recorded and you will not go to court.”