Compression tests of prepared mixtures of varying proportions of ooid and lime mud under continuous and intermittent increase of force to 96,000 lbs (43,636 kg) (equivalent to 7636 psi or 555 kg/cm 2 ) show that ooids may remain undeformed, volume reduction notwithstanding. Survival of undeformed ooids appears to be a function of lime-mud content. A high proportion of lime mud keeps the ooids in a floating dispersed state and force acts isotropically on these particles. Hence a linear relationship exists between increasing proportion of lime mud and proportion of undeformed ooids. As the proportion of lime mud increases that of broken ooids decreases. Hence ooids (and shell fragments) remain unbroken in micritic limestones, even though the original carbonate sediment may have undergone significant compaction. Furthermore grains in a grain-supported sediment are liable to greater degree of deformation than grains in a mud-supported sediment. Deformation of particles may not accompany shrinkage in volume under compactive stress. Experimental compaction resulted in crushed, buckled, faulted, split, spalled, and diagonally fractured ooids. Incremental confining pressure yielded concavo-convex and longitudinal contacts, whereas continuous increase in confining pressure resulted in concavo-convex contacts only. In uncompacted samples all observed grain contacts are point contacts. Prelithification compaction of ooids in carbonate sediments, in contradistinction to deformed lithified rock, rarely displays a homogeneous deformation fabric. Inhomogeneous deformation of grains thus appears to be an important characteristic for distinguishing a fabric generated by overburden compaction of unlithified sediment from that of tectonically deformed rigid rocks.