Process, reactor and burner for the gasification of a hydrocarbon fuel. The burner comprises coaxial channels for the separate supply of an oxidizer gas, a hydrocarbon fuel and a moderator gas. A coaxial channel with the smallest width is bordered by a separating wall with at least one gas exchange. The gas exchange passage can for example be formed by a retracted end of the separating wall and/or by openings in the separating wall.