Published in Petroleum Transactions, AIME, Volume 204, 1955, pages 22–29. Abstract A study of waterflood efficiency, given in terms of oil recovery at water breakthrough and ultimate recovery, has been made on short, consolidated Pyrex glass cores rendered oil-wet by chemical treatment. Contact angle, interfacial tension, permeability and porosity were the variables considered. Oil and water viscosities, core length and velocity of flooding were held constant. The data permit interfacial tension, contact angle, porosity, and permeability to be grouped into a scaling coefficient along with viscosity, velocity of flooding and length of core. Correlation of the scaling coefficient with recovery at water breakthrough is found to follow prediction; correlations of ultimate recovery demand a scaling coefficient different from that which correlates breakthrough recovery. The work indicates that, with proper control, a group of similar natural cores, of permeability plug size, can be correlated to indicate basic flooding performance. Introduction The fraction of oil recovered from a porous medium is related to both reservoir conditions and production techniques. An investigation of all factors that enter into this relationship is necessary in order to arrive at the optimum method of exploitation for oil reservoirs. To define this relationship, laboratory studies have been made by a great many investigators. However, an important obstacle arises if the results of these experiments on water flooding are to be applied to practice. Differences in behavior are to be expected between reservoirs of the dimensions encountered underground and those used in laboratory work. Factors which play an important role under laboratory conditions may be of no consequence in reservoirs. Laboratory operating practices generally differ from field operating practices. Thus, a mere understanding of the mechanism of the displacement of oil by water is not enough. It is just as necessary that the process be analyzed dimensionally to give continuity and validity to the conversion from laboratory to field.