POLICE are now treating a fire at a house in Blackbird Leys as arson.
Five people had to flee the building, in Mallard Close, at about 2.45am.
The fire broke out at around 2.45am on Mallard Close.
A 33-year-old man suffered a broken leg and two men, aged 27 and 48, and two women, aged 20 and 27, were injured.
The officials said the occupants of the house were awakened by the sound of the fire and were forced to jump out of a first-floor window.
Three fire engines from Oxford, with 16 firefighters, arrived at the scene and soon established that all the occupants of the house were out.
They then extinguished the fire using breathing apparatus and three hose lines.
Station manager Simon Belcher said: "They were all so lucky to have escaped with their lives. A working smoke alarm would have warned them much earlier and enabled them to get out much sooner."
Thames Valley Police say it is now being treated as suspicious.
The patients are being treated at the John Radcliffe Hospital.
Anyone with information about the cause of the fire is urged to call DI Louise Roddy via the 24-hour Police Enquiry Centre on 101 or contact the independent charity Crimestoppers anonymously on 0800 555 111, or online at crimestoppers-uk.org.