Police have released CCTV images of a man in connection with five cases of frauds at Sainsbury's stores, including in Aylesbury.
The incidents, which police believe are all linked, took place in May.
Three of them took place at stores in Aylesbury and Maidenhead in Berkshire.
Two other incidents took place outside of the Thames Valley at Stanmore in London and Woking in Surrey.
In each case the thief used cloned bank cards to fraudulently purchase items.
Investigating officer Sergeant Kris Lovell said: “I am keen to speak to the man in these CCTV images, as he may have information which is vital to our investigation.
“If you recognise this man, or have any information in relation to these incidents, please report the details on the Thames Valley Police website quoting reference 43190153359.
"Alternatively, you can call the non-emergency telephone number 101 or contact the charity Crimestoppers anonymously on 0800 555 111."