Spontaneous imbibition is of critical importance to oil recovery from fractured reservoirs. A widely used approach to predict oil recovery involves scab-up of laboratory results to reservoir conditions. Scaling Involves the effects of sample size, shape, boundary conditions, viscosity and viscosity ratios, interfacial tension (IFT), pore structure, wettability, capillary pressure, and relative permeability, This work addresses the application of a characteristic length to scaling the combined effects of sample shape and boundary conditions with only minor variations in other parameters except for liquid/liquid (L/L) viscosity ratios. Imbibition measurements are presented for cylindrical Berea sandstone cores of different lengths. For some experiments, core surfaces were partially sealed with epoxy to give different boundary conditions, Cores were initially saturated with refined mineral oils of different viscosities. A synthetic reservoir brine was used as the wetting phase. The characteristic length is defined as a function of bulk volume, areas of surfaces open to imbibition, and the distances from these surfaces to their respective no-flow boundaries. The characteristic length, in combination with a term that compensates for the effect of L/L viscosity ratio, gave close correlation of all data.