The brawl broke out at about 23:00 BST on Thursday in the Jourdain Road area of Blackbird Leys.
Police officers found a man in his late 20s with serious injuries at the scene, and he later died in hospital. His next of kin have been informed.
Three men and a teenager were arrested on Saturday, and another man was taken into custody on Sunday morning.
Det Ch Insp Mike Lynch said: "We continue to appeal for the public's help in investigating this senseless murder of a man in his 20s."
On Saturday afternoon police said they arrested two men aged 19 and one aged 27, then a 16-year-old boy was held during the evening, and a 23-year-old man the following morning.
All the suspects are from Oxford and remain in custody.
Five people have been arrested on suspicion of murder after a man died following a fight in Oxford.