T E P U R P O S E of this paper is to discuss the recent unclassified information available on the subject of storable liquid propellants. I t is the object of the authors not to provide a handbook of da ta per t inent to the field bu t rather to give the reader a survey t ha t emphasizes the growing importance of storable propellants, recent developments, problems t h a t exist with specific systems, and enough particular information so that , with the aid of the bibliography, an individual can make an accurate judgment of the suitability of available storable propellants for a specific system. This paper will not discuss solid, hybrid, or monopropellant systems; its content deals exclusively with liquid bipropellant systems. The use of hybrids and monopropellants as prime propellant systems is still in the development stage. I t will be, a t best, several years before such propellants will be used in operational vehicles. Furthermore, the more interesting developments concerning these systems do not appear in the unclassified l i terature. Before proceeding, it is desirable to provide a definition for the term "storable ." This is not an easy task, since "storab le" means different things to different people. There would be general agreement, the authors think, t ha t unsymmetrical dimethylhydrazine is a storable and t h a t liquid oxygen is a cryogenic, or nonstorable. The former material is a liquid at room temperature, does not decompose thermally on standing a t even the most extreme ambient conditions, and can be placed into an unvented drum today and be expected to emerge unchanged five years later. Liquid oxygen, however, could certainly not be kept in a d rum with a simple closure for any extended period of t ime. I t could only be kept as a liquid by continuous cooling below —181.8 °F (its critical temperature) . Even a t —181.8°F, the vapor pressure of the material is very high (critical pressure is 7304 CHESTER J. GRELECKI STANLEY TANNENBAUM