Testing samples of oil sands for determining productivity of oil wells and estimating reserves has been described and discussed by many authors. Most articles suggest the use of small 2½-centimeter cubes. Since texture, porosity, and permeability of some rocks, particularly limestone, vary greatly in short distances, very large numbers of small samples are needed to determine even an approximate average permeability, porosity, and fluid content of large slices of rock samples. A discussion is presented of the feasibility and advantages of using large core samples and the effect of several factors such as minute quantities of connate water, presence of traces of emulsions, and presence of certain colloids, on results of fluid-flow measurements in large core samples. T e paper includes tables showing the porosity, permeability, gravity, and fluid content of several oil-bearing formations in Texas.