The APT is almost like a multifactor version of the CAPM. Whereas in the CAPM, everything depends on one factor (that is, the rate of return on the stock market), in the APT there can be multiple factors (such as the rate of return on the stock market, the rate of return from investing in oil, and so on). Both models then say that assets that are more exposed to these risks have to offer higher expected rates of return. Unlike the CAPM, the APT does not necessarily assume that the rate of return on the stock market is one factor. It also does not assume that there is an optimal market portfolio, in which all investors should invest.