A 16-year-old boy has been arrested on suspicion of robbing a bank.
A branch of Lloyds Bank on London Road, Headington, Oxford, was robbed at 10.30am on Friday, Thames Valley Police said.
The teenager, from Oxford, is still in custody.
Another Lloyds in the area was robbed last month when two men - with their faces covered and dressed in blue boiler suits - stole cash from the branch on Stephen Road, Headington, on January 23 at 10.30am.
One of the men was believed to have a firearm and the suspects escaped in a white BMW 1-Series, police said.
Thames Valley Police are appealing for witnesses and information about the robbery on Friday.
Investigating officer Det Sgt Parsons from Force CID in Oxford, said: "I would ask anyone who may not have contacted police already, but has any information about this robbery to get in touch.
"Call 101 with information no matter how minor the detail may appear."
Anyone with information can also call Crimestoppers anonymously on 0800 555 111.