Which types of mergers are likely to be most productive for banks and other financial firms in the US? From a management perspective, mixing disparate firms may be difficult, but may offer significant gains from diversification. The opposite applies to matching similar firms. This paper considers life insurance, property and casualty insurance, securities, and commercial firms as potential matches for banks. It examines a measure of diversification gains from potential consolidation, based on option pricing, and a model of the “building blocks” of the industries, based on arbitrage pricing theory. The results identify potential diversification gains from virtually all combinations involving banking and insurance, which arise because common factors are combined in different ways and because insurance is already well diversified.