The results of the study of organic peroxide-initiated oligomerization of unsaturated hydrocarbons of the C5 fraction, obtained as a by-product of ethane production by gasoline pyrolysis, are presented. The effect of temperature, duration of the process, nature, and concentration of the initiator on the yield and physicochemical parameters of the obtained oligomer was studied. The influence of temperature, process duration, type, and concentration of the initiator on the yield and physicochemical parameters of the oligomer obtained has been determined. The optimum conditions for oligomerization were found to be: temperature 453 K, reaction time 6 h, and concentration of the initiator, di-tert-butyl peroxide (DTBP), 0.05 mol/l. Under optimal conditions, an oligomer is obtained with a yield of 25.8 % w/w (based on raw materials), the physical and chemical parameters of which meet the requirements according to TU U 6-05743160.020-99 “Petroleum-polymer paint and varnish resin synthetic”; and it is suitable for use as a synthetic oil substitute in the production of paints and varnishes, in particular, Oxol.