It has been suggested that a large amount of crustal fluid is trapped at a supercritical state within intrusive rocks beneath volcanoes or calderas near the mountain ranges of northeastern Japan. If we could extract and use these crustal fluids, we could expect to achieve a high level of energy productivity. We have collated field data on high-temperature geothermal areas of the world, used these to produce simple models of their geothermal systems, and then explored their features in terms of the amount of potential power generation. For example, a potential of around 0.1 GW per reservoir over 30 years is expected in northeastern Japan if we consider supercritical reservoirs extending to a 5 km depth.