Bi-directional reflectances of marine liquid water clouds, as measured by the Multiangle Imaging SpectroRadiometer (MISR), are compared with plane-parallel radiative transfer model calculations. We define an angular consistency test that requires measured and modeled radiances to agree within ¿5% for all chosen view angles for the observations to be classified as plane-parallel. When all nine MISR angles are used at the full 275 m resolution, 1 in 6 pixels (17%) pass the test. There is a slight dependence on effective radius Re, with Re = 8 ¿m resulting in the highest pass rate. As the resolution is degraded, clouds appear more plane-parallel, and the passing rate increases to 38% at the coarsest 17.6 km scale. The passing rate quickly decreases as the number of angles used in the angular test increases. Requiring a match at only the nadir and two near-nadir angles immediately eliminates half of the full resolution pixels.