Abstract: Solutions of molecular oxygen in liquid hydrocarbons are prepared by bringing a liquid hydrocarbon into contact with molecular oxygen under superatmospheric pressure in a vertical absorption zone, by a process in which(a) a layer of water is maintained at the lower end of the absorption zone,(b) molecular oxygen is passed into the layer of water,(c) a liquid hydrocarbon is fed in above the layer of water,(d) the finely divided molecular oxygen rising from the layer of water is passed upward together with the liquid hydrocarbon at from 0.degree. to 50.degree. C., with thorough mixing in the absorption zone, with the proviso that no cohesive gas phase is formed, and(e) the solution of molecular oxygen in the liquid hydrocarbon is discharged in the upper part of the absorption zone.