Diagenetic changes can best be observed in the early history of a homogeneous sediment. This study was based upon samples of oolites collected from Southern Florida and the Bahamas that ranged in age from Recent to Pleistocene. On the basis of texture alteration determined by petrographic examination, samples were classified into two major groups, early and later diagenesis, and then studied in detail. In the early diagenesis group, samples varied from unconsolidated oolitic sand to moderately cemented oolitic limestone. Ooid structure was distinguishable thorughout, but become less distinct with advancing diagenesis. There was no significant change in mineral composition, which was essentially aragonite. In the later diagenesis group, stages of alteration were not readily apparent, but samples could be differentiated into alteration types. When ooids were partially replaced by calcite, they took on a soft friable texture; and when replacement was complete, the change was to a denser, vitreous texture. In both groups crystalline calcite formed interparticle cement. Porosity and permeability varied greatly, but moderately good interconnection of porespace prevailed. Diagenesis produced a great diversity in texture, mineral composition, and porosity in the short span of geological time represented by the samples in this study.