PBX9502 is an insensitive high explosive comprising 95% TATB and 5% Kel-F. Like some liquids, the shock velocity—particle velocity relation for non-reacted PBX9502 is initially curved, but tends to a linear relation for stronger shocks. Because of this, the method developed by Jeanloz of finding a Taylor expansion in finite strain form for the principal isentrope cannot be used to develop an EOS. Instead, the principal isentrope for PBX9502 has been found from the Hugoniot by integration, using an analytic form for the variation of Gruneisen Gamma with specific volume. The isentrope has been extended by plausible extrapolations, both beyond the maximum Hugoniot compression and into the expansion regime. Finally an analytic fit has been made to the resulting principal isentrope to develop a Mie-Gruneisen form of EOS for use in reaction rate models. [ABSTRACT FROM AUTHOR]