A static mixer (1)to emulsify water and/or other additives in gas oil comprises a hollow structure (2) within which two mixing units (23,27) are disposed, each comprising a first and a second mixing bodies (24, 25, 28, 29) each carrying a frusto-conical boundary surface (24a, 25a, 28a, 29a). The boundary surfaces (24a, 25a, 28a, 29a) are disposed mutually opposite in parallel and facing each other so as to define a narrow mixing gap (26, 30) of truncated conical form at which the mixture runs in a condition of substantially laminar flow and is submitted to shear forces causing emulsification. Also proposed is a process for producing a dispersion, which process can be carried out by said mixer (1).