NOVELTY - Preparing mixture of Guerbet alcohols, comprises: providing starting material comprising at least one primary alcohol of (I), base and catalyst; mixing starting material with base and catalyst and heating the thus obtained reaction mixture to process temperature above boiling point of water under reaction conditions while removing water; removing at least part of reaction mixture; separating desired Guerbet alcohols from removed part of reaction mixture; and returning other alcohols and optionally other intermediates from the removed part of the reaction mixture to the reaction mixture.    USE - The method is useful for preparing mixture of Guerbet alcohols, where the Guerbet alcohols are used as: additives for fuels; precursors of esters; precursors of gasoline, diesel fuel or aviation gasoline and jet fuel constituents; precursors of surfactants; or precursors of alpha -olefins and their polymers and oligomers (claimed).    ADVANTAGE - The method provides large scale production of multi-branched Guerbet alcohols in an economical manner, while allowing to control the final distribution of Guerbet alcohols by splitting the desired reaction products from the lighter ones and returning the latter into the reaction chamber for further reaction processing.    DETAILED DESCRIPTION - Preparing a mixture of Guerbet alcohols, comprises: providing a starting material comprising at least one primary alcohol of formula (I); providing a base; providing a catalyst; mixing the starting material with the base and the catalyst and heating the thus obtained reaction mixture to a process temperature above the boiling point of water under reaction conditions while removing the water resulting from the thus obtained condensation and dehydration of the primary alcohols; removing at least part of the reaction mixture; separating the desired Guerbet alcohols from the removed part of the reaction mixture; and returning the other alcohols and optionally other intermediates from the removed part of the reaction mixture to the reaction mixture.    R = H or 1-14C alkyl.    An INDEPENDENT CLAIM is also included for a system for synthesizing Guerbet alcohols from a starting material, comprising a reactor (10) adapted for receiving the starting material, the base, and the catalyst to form a reaction mixture, and for heating the reaction mixture to a temperature above the boiling point of water under reaction conditions to obtain a Guerbet condensation and dehydration process, a water separation unit (20) connected to the reactor and adapted to receive from the reactor vapor evolving in the progress of the Guerbet condensation process, and to remove water from the vapor, and an after-treatment system (30, 40) connected to the reactor and adapted to receive from the reactor at least part of the reaction mixture, separating the desired Guerbet alcohols from the removed part of the reaction mixture, and returning the other alcohols and optionally other intermediates from the removed part of the reaction mixture to the reactor.    DESCRIPTION OF DRAWING(S) - The figure shows a simplified piping and instrumentation diagram of the system for synthesis of Guerbet alcohols.    Reactor (10)    Water separation unit (20)    First after-treatment system (30)    Second after-treatment system (40)    Liquid-liquid mixer-settler configuration (41)