Police are investigating the incident which happened at the Wantage supermarket in Limborough Road.
Officers say the victim, a man in his late teens, was approached by a man who sexually assaulted him by touching him over his clothes.
This is said to have happened shortly before 3.10pm on Saturday, July 25.
Thames Valley Police is now releasing a CCTV image of a shopper who officers would like to speak to in connection with the sexual assault investigation.
READ MORE: Utility faces £60k fee over ‘unauthorised’ Oxford slip road closure
Investigating officer police constable Jasmine Moore said: “I am releasing a CCTV image of a man who may have information that could assist our investigation.
“If you are the man pictured, know who he is, or have any information about this incident, please contact Thames Valley Police as soon as possible.
“You can visit a police station, call 101, or make a report via our website, quoting reference number 43260393059.”
