A method for the preparation of olefin polysulfides that can be used in particular as extreme pressure additives for lubricants is described. This method comprises: (1) reacting sulfur monochloride or dichloride with at least one mono-olefin containing 2 to 5 carbon atoms (in general isobutene) resulting in the formation of an adduct; (2) bringing into contact said adduct, conjointly with a hydrocarbyl halide, with a sulfur compound (for example, alkaline sulfides, hydrosulfides or polysulfides) and, in most cases, elemental sulfur, in an aqueous or aqueous-alcoholic medium; (3) heating the mixture and, after it has settled into two phases, separating the organic phase containing the olefin polysulfide; and if necessary (4) treating the product obtained with a base.The olefin polysulfides obtained contain a high proportion of sulfur, have a satisfactory viscosity and are sufficiently soluble in mineral oils as well as synthetic oils to be used as extreme pressure additives in the formulation of gear oils. Some of these products are also advantageous in the formulation of oils intended to be used in metal work.