A coordinated program for the development of improved cements specifically designed for geothermal well applications was continued. Polymer cements (PC) have been identified as promising well cementing materials. Tests indicate that at temperatures above 218/sup 0/C (425/sup 0/C) only PC materials containing mixtures of silica and portland cement are durable to brine and steam. Differential thermal analysis (DTA) studies are underway to determine the reason. Tests are also being conducted on two monomer systems that may further extend the operating temperature range. (JGB)