Use of oxygen for the preparation of an oxygen-containing fluid for use in the treatment of wounds by a method comprising the step of injecting an effective amount of the oxygen-containing fluid selectively and directly into a layer of wound tissue located below a surface layer of said wound. Also provided is an apparatus for injecting an effective amount of an oxygen-containing fluid selectively and directly into a layer of wound tissue located below a surface layer of a wound, said apparatus comprising: a source (1,20,30) of an oxygen-containing fluid selected from gaseous oxygen or water containing at least 10mg per liter of dissolved oxygen； and a microcatheter (9,23,35) in fluid communication with the source of oxygen-containing fluid and having one or more outlet apertures in a tip region thereof, wherein at least a region of the microcatheter (9,23,35) has an effective internal diameter of less than 75 micrometers.
