In this paper, we propose a more flexible “economic cluster identification” approach to analyzing the domestic I/O flows of intermediary goods and service that is based on information theory. Using an “information gain” estimation method, we make efficient use of inequality constraints about the structure of the domestic I/O flows. In particular, it allows us to impose a set of less restrictions than is possible under the traditional methods. The results show that there is a large degree of classification accuracy in South Korea.