Dynastar is a modified starch through pre-gelatinization and biocide treatment. It can be quickly dissolved in cool water to form clear gelatin. When employed in water-base drilling mud, it can reduce fluid loss efficiently. It is shear resistant, salinity tolerant, thermal stable and will not go rotten easily by bacteria. Dynastar can work in many kinds of water-base drilling mud. It is featured by reasonable dosage and relatively low price. So it has good performance/cost ratio. Dynastar fully meets the specification of drill starch stipulated by Section 16, API Spec 13A/ISO 13500.