Empirical longitudinal data on supply relationships between car manufacturers (OEMs) and auto-parts suppliers in the Japanese automobile industry are studied systematically. Such supply relationship formations, which will have emerged over time, are likely to reflect various contingent factors such as industrial conditions (which affect OEMs’ procurement strategies and resulting product demands). There are other important factors such as the level of standardization of the product, and the skills required for manufacturing the product. Furthermore, the effects of such factors may vary from product to product, and year to year. Heterogeneity between the supply networks of various products is elucidated via characterization with several measures, and also via a visualization of the transitions of the network properties. Our systematic analysis of the data provides profound insight into how product markets may have become stabilized or more competitive, and how the market selection process may affect the evolution of the supply network characteristics. The proposed approach and findings of the study can contribute to supply network modeling, and lead to the prediction of future changes in product markets, as well as suppliers’ production strategy planning.