A petroleum belt extends from southern Saghalien and Hokkaido to Nagano Prefecture in Honshu Island, along the coast of the Japan Sea. Besides, there are small fields of Shizuoka Prefecture in Honshu and the Island of Taiwan (Formosa). Petroleum deposits in Japan are found exclusively in marine Neogene formations. The chief oil fields in Hokkaido are those of Masuhoro, Ishikari, and Yufutsu, of which Yufutsu is the most important. In the Prefecture of Akita, the oil fields of Kurokawa, Toyokawa, Michikawa-Asahigawa, and Oguni are noteworthy, though at present their aggregate production amounts to only about 108,000 kiloliters a year. The oil fields of Niitsu, Nishiyama, and Higashiyama in Niigata Prefecture have been worked since about 39 years ago and their total product on together with that of minor fields in the vicinities amounted to about 360,000 kiloliters in 1914. Since then the production gradually diminished and was only about 192,000 kiloliters in 1930. In Taiwan, the only field which is now productive is that of Byoritsu. Others are expected to be developed in the future.