As a part of a wider study of the hydraulic properties of Upper Cretaceous chalk from East Yorkshire and the North Sea, a method of pore space casting is being employed. Thus, with the aid of the Scanning Electron Microscope it is possible to obtain by direct visual observation information about the shape and size of pores and grains, the connectiveness and roughness of pore channels, the presence of clay and silicate minerals, and other factors that together control fluid flow in porous rocks. A more detailed understanding of the nature of hydrocarbon or water-bearing rock is becoming increasingly important in pursuance of studies of oil exploration, oil exploitation, and geotechnics. In this paper a method of impregnation and casting the pore space in chalk is described, together with some preliminary observations of chalk pore geometry.