A fundamental question exists regarding how well information about ocean processes can be extracted from a time series of cw acoustic phase and amplitude when the propagation channel consists of multiple acoustic paths. In this paper, it is shown that there are at least two multipath propagation conditions under which an acoustic cw propagation experiment can be used to measure properties of the sound‐speed field and the ocean processes along the propagation path: narrow‐band (frequency‐modulation) path‐length modulation of all paths, and wide‐band (frequency‐modulation) path‐length modulation of a dominant path. A dominant path is one with power which exceeds the power on all other paths plus noise by at least 6 dB. Signal processing techniques for measuring the fluctuation spectra in both multipath situations are described and performance estimates are derived. The factors which limit how well information can be extracted are discussed.