Abstract: In accordance with the present invention, a microbial polysaccharide having the features characteristic of S-657 has been found to be effective to improve the rheological properties of a variety of cementitious systems. Thus, the addition of a small, but effective amount of S-657 to such cementitious systems as portland cement, self-leveling grouts, fresh or saltwater oil well cement slurries, microfine cements, and the like, gives rise to substantial improvements in such properties as bleed, flow resistance, fluid loss control, and the like. S-657 addition provides enhanced rheological control in a variety of cementitious systems. In addition, S-657 provides a number of advantages relative to prior art systems, including improved free water and sedimentation control, as well as reduced fines loss during underwater placement.