TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Parameter: The molar ratio alcohols+alkyl ethers/isobutene is lower than 0.7. The reaction is carried out at 30-120degreesC, at lower than 5 MPa, and at feeding space velocities lower than 30, preferably 1-15 hours-1. Preferred Component: The linear alcohol has 1-6C atoms. It is methanol (17, 18) and/or ethanol. The branched alcohol has 4-7C atoms. It is tert-butyl alcohol or tert-amyl alcohol. The alkyl ether has 5-10C. It is methyl tert-butyl ether, ethyl tert-butyl ether, methyl sec-butyl ether, ethyl sec-butyl ether, methyl tert-amyl ether, and/or ethyl tert-amyl ether. Preferred Process: Other possible olefins present in the charge react to form high-octane products. Isobutene content in the charge is modified by dilution with 4-7 streams. The process comprises feeding 45C hydrocarbon cut containing isobutene, together with stream(s) containing oxygenated products (15, 16) (linear and branched alcohols, ethers, and water), to reaction step(s) (consisting reactor(s)); separating the 4C/linear alcohol azeotropic product and possibly the 4C products from the 5C hydrocarbons, from the remaining oxygenated products and from the hydrocarbon product in distillation column(s); recovering the linear alcohol from the azeotropic mixture with the 4C products by conventional processes such as washing with water or absorption on inorganic solids; separating the 5C hydrocarbons, as an azeotropic compound with the branched alcohol, from the remaining oxygenated products and from the reaction product, in fractionation column(s), to obtain three streams with the desired purity; recycling the streams containing the oxygenated products (branched alcohol and ether) and the linear alcohol recovered, to the two reaction steps; feeding linear alcohol and water (which forms the branched alcohol in the reactors by reaction with the tertiary olefin) to the reaction steps to compensate the losses of linear alcohol, which can react with the dimers and linear 4C olefins, and branched alcohol which, on the contrary, leaves the plant together with the 5C products; and recycling part of the 4C products, with or without linear alcohol, to the reaction steps to maximize the isobutene conversion. The separation of the 5C/branched alcohol azeotropic product (19) can be carried out starting from blends of: 5C-oxygenated products (ethers and branched alcohols)-reaction product, where 5C hydrocarbons are recovered as an azeotropic compound with the branched alcohol as head effluent using a scheme based on a column, with recovery of the remaining oxygenated products as side cut, or two fractionation columns; 5C-oxygenated products (ethers and branched alcohols)-dimers, where 5C hydrocarbons are recovered as an azeotropic compound with the branched alcohol as head effluent of a fractionation column; 4-5C-oxygenated products (ethers and branched alcohols)-reaction product, effluent from a reaction step, where 5C hydrocarbons are recovered as an azeotropic compound with the branched alcohol as side cut of a fractionation column from whose head the 4C/linear alcohol azeotropic product and possibly the 4C products are recovered, where mixture containing the oxygenated products and the reaction product is recovered at the bottom; 4-5C-oxygenated products (linear and branched alcohols) where 5C hydrocarbons are recovered as an azeotropic compound with the branched alcohol as bottom effluent of a fractionation column from whose head the 4C/linear alcohol azeotropic product and possibly the 4C products are recovered. The 5C/branched alcohol azeotropic mixture is joined to the reaction product. The dimerization reaction is carried out in fixed bed, tubular, and/or adiabatic reactors.