At around 12.30am on Monday (29/1) a man wearing a face covering entered the Esso garage, Berkeley Avenue, Reading, and threatened a member of staff.
The offender, who was armed with a knife, demanded cash from the tills.
He stole a quantity of cash and tobacco.
The member of staff present was not injured during the incident.
Detective Constable Marius York, of Reading Force CID, said: “Detectives are investigating this robbery and I would like to speak to anyone who has any information which could help us with our enquiries.
“Any information you have should be reported to us by calling our 24-hour non-emergency number 101.”