Publication Rights Reserved This paper was presented at the University of Oklahoma-SPE Production Research Symposium in Norman, Okla., April 29–30, 1963, and is considered the property of the Society of Petroleum Engineers. Permission to published is hereby restricted to an abstract of not more than 300 words, with no Illustrations, unless the paper is specifically released to the press by the Editor of the Journal of Petroleum Technology or the Executive Secretary. Such abstract should contain conspicuous acknowledgement of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request providing proper credit is given that publication and the original presentation of the paper. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. Abstract The measurement of pore space volumes in small cores is commonly accomplished by immersing the cores in a liquid, so that all air other than that contained within the pore space in the core can be readily expelled from the apparatus. Then, after sealing the apparatus, the pore volume can be measured by expanding the air which had been contained in the pores. Mercury is commonly used for this purpose. However, there are some objections to the use of mercury, one being that after such measurements are completed some mercury usually is left within the core so that it is not suitable for further experimental determinations of rock properties. This paper presents the experimental results obtained when using lubricating oil rather than mercury for immersing the cores in making the pore volume measurements. The common calibrated plunger type of apparatus was used. Tn testing one group of cores, the viscous nature of the Oil was the only different limiting the entry of oil into the pores. In testing a second group of cores, the cores were chilled and the pores were sealed by dipping the cores into wax-bearing oil so that wax congealed on their surface before they were immersed in oil in the porosimeter. Finally, the pore volumes of all cores used were measured by immersing the cores in mercury in the customary manner. Excellent agreement was obtained between the pore volumes measured by the two methods, particularly for the second group of cores, where the pores were sealed with wax when oil was used, as compared to the pore volumes measured when the same cores were later immersed in mercury. Introduction The work described in this paper was concerned primarily with the measurement of the volume of the interconnected pores within small core samples, as they exist under surface conditions in the laboratory. Tn general, when determining porosity, which is expressed as a fraction or percentage of the bulk volume, it is desirable to obtain a measure of the pore volume within the rock specimen. By definition the pore volume is the difference between the bulk volume and the volume of the solid mineral framework, and by mathematical relations the determination of any two of these quantities permits the calculation of the porosity. However, where the pore volume is essentially calculated as the difference between the bulk volume and mineral volume, relatively small percentage errors in either or both of these can result in larger errors in the calculated value of porosity. This condition becomes more severe as the pore fraction becomes smaller and consequently the values of bulk volume and mineral volume approach each other.