Which type of account administration includes the commingling of several accounts administered by the trust department?

The correct answer, collective investment fund services, refers to a type of account administration where the assets from multiple accounts are pooled together for investment purposes. This approach allows for diversified investment options and can lead to cost efficiencies, as the trust department can achieve economies of scale by managing a larger fund rather than individual accounts.

In collective investment funds, various clients' assets are combined, which can enhance investment opportunities that may not be available to smaller investment accounts. This method is particularly beneficial for investors who seek broader market participation or who want to invest in a diversified portfolio without needing to manage individual asset allocations actively.

Options related to employee benefit services, personal trust and agency services, and corporate trust services do not primarily focus on the commingling of multiple accounts. Employee benefit services generally involve managing specific accounts for employee retirement plans or benefits. Personal trust and agency services typically deal with managing and administering trusts for individuals, focusing on their personal assets separately. Corporate trust services tend to center around managing securities and ensuring compliance for corporate clients rather than pooling funds from various individual accounts.