Operational synergy in the US electric utility industry under an influence of deregulation policy: A linkage to financial performance and corporate value

►The synergy effect has not existed in the operational performance of diversified utility firms before and after the deregulation on the US electricity markets. ►Core business concentration is more effective for electric utility firms than corporate diversification to enhance their operational performance under the current US deregulation policy. ►The operational performance has had an increasing trend until 1996 and a decreasing trend after 1996. ►The US deregulation policy has been influential on their operational performance. ►The enhancement in operational performance of electric utility firms has improved their financial performance. ►The improvement in financial performance has increased their corporate value.