This paper presents characteristic studies that should be considered in oil and gas field developments. Several significant articles are illustrated and discussed, covering the following items; (1) reservoir rock properties, (2) waterflooding, (3) underground natural gas storage and (4) petroleum reserves and techno-economics. The effects of clays and clay minerals on relative permeability curves are clarified. The new porosity measurement of shaly sand cores is devised. At the planning stage, A and B blocks in Sarukawa oil field were given the priority of waterflooding projects by means of application of reservoir engineering data, in addition to the usual geological and geophysical information. The reservoir engineering study on Sekihara gas field has contributed to research for underground natural gas storage. The proposed procedure on moving boundary problem may be required in relatively smaller reservoir. The developed probability model on estimation of oil reserves and techno-economical appraisal method are discussed.