Clothing store Next is offering a £10,000 reward to anyone who can help staff catch the man who dressed as Santa to rob its Cowley branch.
The knife-wielding robber threatened staff at the Oxford Retail Park store on December 23 before fleeing with cash on a bicycle.
Police described the suspect as a white man in his 30s, of medium build and about 5ft 9ins to 6ft tall.
He wore a blue fleece and jeans under the Father Christmas outfit.
Next is offering the reward for information leading to the conviction of the robber.
Anyone with information should call Det Sgt Mark Stalder on 101.