TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractStatic bottles tests have been conducted on model naphthenic acid solutions with the objective of studying the mechanisms of naphthenate "scale" formation. Various experimental sensitivities were analysed such as initial pH, cation type and concentration in the aqueous phase, naphthenic acid type and concentration in the oil phase. Data has been obtained for the deposits formed from sodium, calcium and barium rich aqueous phases and their combinations. Trends in precipitate mass as well as the composition of the solid deposits obtained from X-Ray diffraction (XRD) and electron microscopy/ energy dispersive x-ray (ESEM-EDX) are presented. The effects of cations on bulk and surface properties such as viscosity, emulsion stability and interfacial tension are also shown. These results contribute to the understanding of naphthenate deposition mechanisms under lab conditions.