The use of multiple geophones, which has been largely empirical, serves two primary functions: cancellation of random and other unwanted energy, and improved sampling of the wave front. Curves are presented showing effectiveness of several different spreads for surface-wave cancellation. The results also apply to mixed records. Cancellation of random energy follows conventional sampling theory, varying with the square root of the number of geophones in the spread. Sampling of the wave front is more complex because the samples are not mutually independent.