Information about bridge structure and functionalities has been considered to be crucial in estimating the reactivity of coals, and the purpose of this study is to improve the validity of the RICO technique in the determination of aliphatic bridges and functional groups using a Japanese Taiheiyo coal. It was found that room temperature, which had been commonly employed previously, is insufficient for efficient oxidation kinetics and higher temperature such as 40 degrees C increased the oxidation kinetics 2-fold. Candidates for the remarkable amounts of resolved aliphatic polycarboxylic acid products are thought to be the corresponding polyaryl-substituted aliphatic cross-linkages and various hydroaromatic species. Remarkable amounts of polymeric aliphatic fraction were also formed after RICO. Much higher amounts of benzenepolycarboxylic acids were recovered, and significant improvement of carbon mass balance was achieved contrary to previous reports.