The existing viscosity-concentration equations for concentrated emulsions of nearly spherical noncolloidal droplets are first reviewed. The equations of emulsion relative viscosity eta (r) vs volume fraction of dispersed-phase 0 existing in the literature are characterized as single-parameter equations because viscosity ratio (ratio of dispersed-phase viscosity to continuous-phase viscosity) is the only parameter in the equations. The equations are evaluated in light of a large body of experimental data for concentrated emulsions, covering a broad range of viscosity ratios. The existing equations generally give good predictions of relative viscosity only at low values of phi (phi < 0.2). Several new equations are proposed and evaluated with experimental data. The proposed eta (r) VS phi equations are characterized as two-parameter equations because they contain two parameters, namely, the viscosity ratio and phi (m), the maximum packing volume fraction of droplets. The proposed equations generally show good agreement with the experimental data.