American Capital Agency Corp is a real estate investment trust that invests primarily in agency mortgage-backed securities, or MBS, on a leveraged basis. The firm's asset portfolio is comprised, cumulatively, of residential mortgage pass-through securities, collateralized mortgage obligations, or CMO, and nonagency MBS. Many of these are guaranteed by government-sponsored enterprises. The majority of American Capital's investments are fixed-rate agency MBS. Most of these are MBS with a 30-year maturity period. The counterparties to most of American Capital's assets are located in North America. Counterparties in Europe also represent a significant percentage of the company's total portfolio. American Capital derives nearly all its revenue in the form of interest income.