A robber asked his victim to lay on the floor as he raided the safes.
It happened at the Co-Op in Wood Lane, Sonning Common, on Sunday night.
Police say a man armed with a knife, threatened two members of staff at around 10pm
He told one of them to take him to the safes and ordered the other to lay on the floor.
The suspect then took a load of cash and told both victims to lay on the floor and wait for one minute - before running off.
Police have now released CCTV images of a man they want to talk to in connection with the incident.
Investigating officer Detective Sergeant Alun Watkins, of Force CID at Abingdon, said: “This was a very frightening incident for the victims, and we believe this robbery is linked to a number of similar offences across the three counties of the Thames Valley.
“I am appealing to anybody who recognises the man in the images to contact Thames Valley Police on 101, quoting reference number 43180104891, or anonymously call Crimestoppers on 0800 555 111.”