A chemical oxygen generator has a chemical mixture based on an alkali-metal chlorate (NaClO.sub.3) which constitutes the charge of a cartridge having an ignition device and an oxygen outlet. This oxygen generator is improved so that the charge is insensitive to shock and so that it can be configured in any desired outer form and size and that an advancing reaction zone is assured without a further assisting device. The charge includes a tight bed of chemical pellets which lie one against the other to form the smallest possible contact surfaces.