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The producing reservoirs of the Ojiya oil eld, Niigata Prefecture, which belong to the Uonuma Group in the northern part（Yamaya area）and the Haizume Formation in the southern part（from Jigokudani to Kirikubo areas） , are correlated to the Nishiyama stage in the Niigata well stratigraphy.Head space gases from the MITI † Oguni explorator y well and surface seepage gases are mainly thermogenic origin based on their carbon isotopes, whose maturity is estimated to be 1.0 to 1.1 ％ Ro equivalent, and were probably generated in the Lower Teradomari Formation below 4,000 m in depth.As oil properties such as speci c gravity and distillation test result are clearly different between the Yamaya oil and the others（the southern oil） , the Yamaya pool is separated from the others. The southern oil geochemically resembles the Sagara oil, Shizuoka Prefecture, which indicates that the oil were generated in the deeper part of the basin, migrated upward through faults, laterally migrated passing through the gas showing inter vals in the MITI Oguni well, and accumulated. The Yamaya oil was probably migrated through the reverse fault in the Nishiyama Formation of the Ojiya SK-1 and SK-2 wells.