Increased oil exploration necessitates building of conc~ete structures for its production and storage. The effects of crude oil on concrete properties are not well known and little data is available in the published works. This investigation covers HCP, mortar and concrete. First, it studies the effects of cracking and direction of casting on the flow of water or oil of different constitutions through concrete storage tanks. Secondly, it studies the relationships between the pore structure and permeability of HCP, mortar and concrete as influenced by w/c ratio, hydration and aggregate content. OPC was used for the tests. Experimental results show that, in concrete specimens, the flow of water through cracks is generally greater than the flow of crude oil through the same type of cracks. Sorptivity can predict reasonably accurately the flow of liquids and is useful in characterizing the flow of various oil types th:r:( ,ugh HCP, mortar and concrete. No specific oil property appears to control the oil flow through cement composites. Concrete tanks should be lined when used for storing diesel and parafin. Crude oil flow through concrete tank wall was found to be 1.06 - 1.81 times flow through the tank floor. Increasing the w/c ratio, increases the total porosity, pore surface area and threshold radius but decreases the density and does not effect the hydraulic radius. Increasing the age of HCP (w/c = 0.7) from 7 days to 6 months decreases the total porosity, pore surface area, threshold radius and hydraulic radius by 12%, 19%, 71% and 9% respectively, but increases the density by 13%. Adding sand to HcP, reduces the total pore volume and the pore surface area but increases the density. Wax deposits from the crude oils blocked all pore radii <650A, which is called the "critical pore radius" (Pcr). Saturation in crude oil appears to alter the internal structure of the cement composites. Dry curing increased most pore parameters but decreased the strength of the mortars. Permeability of mortar and concrete increases with w/c ratio, applied pressure, aggregate volume concentration and drying temperature but decreases with the test period and hydration. permeability was found to relate reasonably accurately to pore structure using Kozeny's theory provided the pore parameters are for pores of radii >650A.