A process for oxidizing cumene to cumene hydroperoxide using an oxygen containing gas, which process comprises: - conducting a cumene feed and an oxygen containing gas feed to at least the first oxidation reactor in a series of 3-8 reactors, thereby forming an oxidation mixture, and - conducting the oxidation mixture from one oxidation reactor to at least one subsequent reactor, wherein - the reactors are operated with reducing liquid levels; - the oxidation is operated as a dry oxidation, whereby the only gaseous feeds conducted to the oxidation reactors are the cumene feed and the oxygen containing gas feed; - the oxygen containing gas feed is washed with caustic and then with water to remove all acidic or caustic traces before conducting it into an oxidation reactor; - the pressure within each oxidation reactor is in the range of 0-10 barg; - the off-gases from the top section of each oxidation reactor are separated and cooled, whereby a condensate containing unreacted cumene is formed, and - washing the condensate and recycling at least a part of it to at least the first oxidation reactor; - the non-condensed off-gases are treated in a thermal oxidizer; and - the first reactor in the series of oxidation reactors has a liquid inventory of 30-300% larger than in the remaining reactors, or the first two reactors in the series of oxidation reactors have a liquid inventory of 30-300% larger than in the remaining reactors; and wherein the first reactor or the first two reactors are larger than the other reactors; reactor(s) with the larger liquid inventory are the same size; and reactor(s) with lower liquid inventory are the same size. - conducting a cumene feed and an oxygen containing gas feed to at least the first oxidation reactor in a series of 3-8 reactors, thereby forming an oxidation mixture, and - conducting the oxidation mixture from one oxidation reactor to at least one subsequent reactor, wherein - the reactors are operated with reducing liquid levels; - the oxidation is operated as a dry oxidation, whereby the only gaseous feeds conducted to the oxidation reactors are the cumene feed and the oxygen containing gas feed; - the oxygen containing gas feed is washed with caustic and then with water to remove all acidic or caustic traces before conducting it into an oxidation reactor; - the pressure within each oxidation reactor is in the range of 0-10 barg; - the off-gases from the top section of each oxidation reactor are separated and cooled, whereby a condensate containing unreacted cumene is formed, and - washing the condensate and recycling at least a part of it to at least the first oxidation reactor; - the reactors are operated with reducing liquid levels; - the oxidation is operated as a dry oxidation, whereby the only gaseous feeds conducted to the oxidation reactors are the cumene feed and the oxygen containing gas feed; - the oxygen containing gas feed is washed with caustic and then with water to remove all acidic or caustic traces before conducting it into an oxidation reactor; - the pressure within each oxidation reactor is in the range of 0-10 barg; - the off-gases from the top section of each oxidation reactor are separated and cooled, whereby a condensate containing unreacted cumene is formed, and - washing the condensate and recycling at least a part of it to at least the first oxidation reactor; - the non-condensed off-gases are treated in a thermal oxidizer; and - the first reactor in the series of oxidation reactors has a liquid inventory of 30-300% larger than in the remaining reactors, or the first two reactors in the series of oxidation reactors have a liquid inventory of 30-300% larger than in the remaining reactors; and wherein the first reactor or the first two reactors are larger than the other reactors; reactor(s) with the larger liquid inventory are the same size; and reactor(s) with lower liquid inventory are the same size. wherein the first reactor or the first two reactors are larger than the other reactors; reactor(s) with the larger liquid inventory are the same size; and reactor(s) with lower liquid inventory are the same size.