The writer visited to Taiwan in April 1953 and spent about 110 days in studying the subsurface structure of the now-producing oil and gas fields; namely from the north, Chuhuangkan oil field, Chinsui gas field. Niushan gas field and Chutauchi structure. In the Chuhuangkan oil field and Chinsui gas field, he has carried out subsurface investigation to field out whether there is any room for drilling or the possibility of extension wells. In Niushan gas field the possibility of deepening chiefly, and in Chutauchi structure the extension wells have been investigated. The results of thsse investigations are as follows; Chuhuangkan Oil_ Field: -There is possibility, in southern district, for more exploration wells and exist several deepening wells. Chinsui gas field: -Extension well is needed in the southern district. Niushan gas field: -Expectation of deepening was judged to have been small. Chutauchi structure: -Great hopes are entertained of this field as has no exploration been carried out in this structure.