The Matsukawa geothermal power station has continued successful power generation since 1966. The wells and reservoir have shown a very slow decline, which is a result of appropriate station sizing and adequate operational criteria. The power plant was sized only to meet the demand of the company's factory for its in-house electric use, instead of full utilization of the resource. The power plant has been operated so as to maximize the profit instead of insisting on operating continuously at full power. A proper understanding of the reservoir has helped to maintain stable operation. Station sizing (23.5 MWe since 1993) appears to be the most important factor in the successful development and operation of the Matsukawa geothermal field. The Matsukawa development is an example of the successful application of the MiniMax principle to the development of a geothermal project. (C) 2003 CNR. Published by Elsevier Science Ltd. All rights reserved.