Oxygen burner (1) used in high temperature processes comprises an inner tube (2) for delivering fossil fuel and a double-walled outer tube (4) concentrically arranged around the inner tube and delivering oxygen. Drive devices axially adjust the inner and outer tubes relative to each other. Preferred Features: A spindle adjusting motor (7) attached to the inner tube on the feed side has a drive spindle (8) connected to one end of the outer tube on the feed side. The fossil fuel is natural gas and the inner tube has a connector (3) for connecting to a natural gas supply. A connector (5) on the outer tube is connected to an oxygen supply