A standard technique for determining the dispersion coefficient and dispersivity has been developed in this study. By using the dispersion measurement techniques as described in this paper, the extent of unsteady mixing of a resident fluid with the injected fluid in an oil reservoir rock can be determined. Dispersivities of several Berea sandstone cores were experimentally determined and attempts were made to correlate dispersivity and dispersion characteristics with other rock characteristics. The most significant and direct relationship of the dispersion characteristics was found to exist between the dispersion coefficient and the total permeability of a core. A correlation has also been developed to correct the viscosity effect of the displacing and the displaced fluid on the dispersivity of a reservoir rock. Average grain diameters of several Berea cores were determined by sieve analysis and correlated with the dispersion coefficients and dispersivities of the corresponding core samples. The dispersion coefficients and dispersivities of the Berea sandstone cores were found to increase with the increasing grain size. 15 refs., 9 figs., 4 tabs.