To clarify validity of an evaluation method using reservoir simulators, an application survey is made in the Oguni area, Kumamoto Pref. The observation analysis continued since 1990 revealed that there is a wide high water-permeable zone in the reservoirs north of the area. Also, data on pressure interference tests performed by combining production well and injection well confirmed that there is a non-permeable zone which divides the reservoirs between south and north. The fluid geochemical analysis makes grasp of fluid flow tighter. It was found out that there is a possibility of more than one heat history in the area, from the distribution of two peaks of the fluid inclusion filling temperature. Reservoir models by the thermal water single-phase simulator agree well with the measured temperature/pressure. Steam-thermal water two-phase state concept models by the gas-liquid two-phase simulator are well correspondent to the measured shallow-area temperature/pressure interference test data. By these natural state reservoir models, the overall production predicting evaluation is made possible. Moreover, by fracture models, a behavior of fractured reservoirs can be quantitatively evaluated. 32 refs., 110 figs., 27 tabs.