Abstract Laboratory results of oil recovery through spontaneous imbibition are commonly scaled-up to forecast oil recovery from fractured reservoirs. This study addresses oil recovery from cylindrical sandstone cores by spontaneous imbibition at very strongly water-wet conditions for viscosity ratios of unity (a special case of the Mattax and Kyte scaling condition that viscosity ratios be matched). Combinations of mineral oils and aqueous solutions of glycerol were used to obtain matched viscosities ranging from 4 to 172 cp. In all, 25 imbibition data sets are reported for boundary conditions of all core faces open, two ends closed (radial imbibition), and one end open (linear imbibition). The data sets for individual boundary conditions were satisfactorily correlated by the Mattax and Kyte scaling group. Overall correlation of results was obtained after compensating for different boundary conditions by means of a characteristic length. An obvious limitation of correlations based on linear scaling of time is that differences in the shapes of imbibition curves cannot be eliminated. The correlated data provides clear distinction between the overall shape of recovery curves for linear versus radial imbibition. Final oil recoveries for radially dominated imbibition were independent of viscosity whereas recoveries for linear imbibition were consistently lower and decreased by up to 2.5 % PV with increase in viscosity. Shortly after the onset of imbibition, oil recovery for linear flow is generally close to linearly proportional to the square root of time until the imbibition front reaches the end of the core.