The electrodes in a coupled multielectrode array sensor (CMAS) are usually flush-mounted in an insulator, and the spacing between adjacent electrodes is an important parameter. The common belief is that the smaller the spacing is, the better the multielectrode array simulates the behavior of a real one-piece metal. Experiments were conducted to study the effect of spacing in CMAS on the measurements of corrosion rates. The data suggest that the spacing has no significant effect on the measured nonuniform corrosion rate for carbon steel in simulated seawater when the spacing varies from 1 to 8 mm. Preliminary studies also suggest that the CMAS with 16 closely packed electrodes and small spacing (0.05–0.25 mm) may measure a lower than usual nonuniform corrosion rate because of the efficient chemical interaction among all of the electrodes packed within a small area. The efficient chemical interaction may have caused all the electrodes in the small area to be under active corrosion such that there were no effective cathodic electrodes left to support localized corrosion. This was evidenced by the measurement of the open-circuit potentials of individual electrodes soon after decoupling of the electrodes. The data showed that there is a small variation in the open-circuit potentials for the probe with closely packed electrodes (small standard deviation). In contrast, the standard deviations for the probes that have a spacing of 1 or 8 mm were larger. As a sensor, the loss of effective cathode may not represent the situation for industrial equipment where the cathodic sites in faraway locations may always be available when there is localized corrosion.