Process and apparatus for enriching liquids with oxygen by means of a catalyst and a liquid which gives off oxygen under the effect of that catalyst. The process involves passing the oxygen-yielding liquid through a porous molding, in the pores of which the catalyst is incorporated in known manner, thereby giving off oxygen, the side of the porous molding which gives off a greater quantity of oxygen being in contact with the liquid to be enriched with oxygen. The oxygen-yielding liquid is passed through the porous molding under its own static pressure, or under the effect of the excess pressure built up in the container through the formation of oxygen. Preferred embodiments include use of a 0.1 to 5% solution of hydrogen peroxide as the oxygen-yielding liquid; using ruthenium oxide or hydroxide as the catalyst. The apparatus for carrying out the process includes a storage vessel containing the liquid which gives off oxygen under the effect of a catalyst, connecting means, and a porous molding connected thereby to the storage vessel and containing the catalyst, the molding being completely immersible in the liquid to be enriched with oxygen. Alternatively, the storage vessel and the porous molding can be dipped into the liquid to be enriched with oxygen, so that at least the entire molding is immersed. Preferred embodiments include the porous molding being a tube having at least one empty space extending over its entire length, one end tightly sealed and the other end tightly connected to the storage vessel; the porous molding being a hollow body having an empty space with an internal diameter of at least 0.5 mm extending over its entire length; the porous molding being of polypropylene, MgO, Al.sub.2 O.sub.3 or clay; use of a metering pump for adjusting the supply of oxygen-yielding liquid; and provision of a vent connected to the porous molding.