The call options theory of corporate security valuation is applied to narrow-banking contingent claims of one bank, while the cap options theory is applied to synergy-banking contingent claims of another bank. This article investigates efficiency gains specified as equities of scope associated with the likelihood of the two banks involved in merger under capital regulation. We find that merger incentives are encouraged when the narrowing banking is conducted by the consolidated bank, whereas discouraged when the synergy banking is conducted. Raising bank capital requirement leads to an increased interest margin of the consolidated bank with the narrow banking valuation; however, to a decreased margin of the consolidated bank with the synergy banking valuation. An increase in the capital regulation reduces the merger incentives in the narrow banking valuation whereas increases the merger disincentive in the synergy banking valuation. These findings are consistent with the organizational theory that predicts a comparative advantage of narrow banking proposals in bank mergers.