In the production of lubricating oils by the condensation with aluminium chloride or like condensation agents of benzines rich in unsaturated hydrocarbons produced by the catalytic conversion of mixtures of hydrogen and carbon monoxide, the condensation agent is used in a quantity which is insufficient for complete conversion in a single temperature stage and the condensation temperature is raised gradually, continuously or in stages, during the conversion, while the conversion agent separated off after the reaction is completed is used for the conversion of a new charge of benzine commencing again at a low temperature. The conversion agent, which is reduced in effectiveness after one or more conversions may be regenerated by the addition of small quantities of fresh conversion agent as described in Specification 473,935. Benzines rich in unsaturated hydrocarbons are preferably obtained by the cracking or catalytic dehydrogenation of the products boiling above 100 DEG C. obtained by the catalytic conversion of mixtures of hydrogen and carbon monoxide. The condensation temperature may be controlled by absorbing the heat generated in the reaction by adding neutral low-boiling hydrocarbons, e.g. propane, butane, pentane to the reacting materials, the vaporized oils being condensed and returned to the reaction vessel. 1000 Gs. of a cracked benzine containing 45 per cent unsaturated hydrocarbons was mixed with 10gs. anhydrous aluminium chloride and subjected to a reaction temperature rising from 20 to 100 DEG C. during the course of 120 hours. After the reaction had ceased the layer of benzine containing the lubricating oil was separated from the contact layer and 424 gs. lubricating oil were recovered by distillation. The contact layer, after an addition of 10-20 per cent of the quantity of aluminium chloride first added, was used to convert a fresh charge of benzine commencing again at 20 DEG C.ALSO:In the production of lubricating oils by the condensation with aluminium chloride or like condensation agents of benzines rich in unsaturated hydrocarbons produced by the catalytic conversion of mixtures of hydrogen and carbon monoxide, the condensation agent is used in quantity which is insufficient for complete conversion in a single temperature stage and the conversion temperature is raised gradually continuously or in stages during the conversion, the conversion agent separated off after the conversion being then used for the conversion of a fresh charge of benzine commencing again at low temperature. The conversion agent, which is reduced in effectiveness after one or more treatments, may be regenerated by the addition of small quantities of fresh conversion agent as described in Specification 473,935, [Group III]. The condensation temperature may be controlled by absorbing the heat generated in the reaction by adding neutral low-boiling hydrocarbons, e.g. propane, butane, pentane. 1000 gs. cracked benzine was mixed with 10 gs. aluminium chloride and treated at a temperature rising from 20-100 DEG C. in 120 hours. The benzine layer containing the lubricating oil was separated from the contact layer and 424 gs. lubricating oil were recovered by distillation. The contact layer after addition of 10-20 per cent of the quantity of aluminium chloride first added was used to convert a fresh charge of benzine commencing again at 20 DEG C.