We study the relation between monthly mean albedo and cloud fraction over ocean,60∘S–60∘N. Satellite obser vations indicate that these clouds all fall on the same near-exponential curve,with a monotonic distribution over the ranges of cloud fractions and albedo. Using these observational dataas a reference, we examine the degree to which 26 climate models capture this feature of the near-globalmarine cloud population. Models show a general increase in albedo with increasing cloud fraction, but noneof them display a relation that is as well defined as that characterizing the observations. Models t ypicallydisplay larger albedo variability at a given cloud fraction, larger sensitivity in albedo to changes in cloudfraction, and lower cloud fractions. Several models also show branched distributions, contrasting with thesmooth observational relation. In the models the present-day cloud scenes are more reflective than thepreindustrial, demonstrating the simulated impact of anthropogenic aerosols on planetary albedo.