diff --git a/Cantera/src/thermo/PDSS_HKFT.cpp b/Cantera/src/thermo/PDSS_HKFT.cpp
index 2bd59bf00..f2975c5fb 100644
--- a/Cantera/src/thermo/PDSS_HKFT.cpp
+++ b/Cantera/src/thermo/PDSS_HKFT.cpp
@@ -836,6 +836,12 @@ namespace Cantera {
 
       return dfac1dT + dfac2dT + dfac3dT;
 
+    } else if (ifunc == 3) {
+      double beta   = m_waterSS->isothermalCompressibility();
+
+      double dgdp = - bfunc * gval * dens * beta / (1.0 - dens); 
+      
+      return dgdp;
     } else {
       throw CanteraError("HKFT_PDSS::gg", "unimplemented");
     }
diff --git a/Cantera/src/thermo/PDSS_HKFT.h b/Cantera/src/thermo/PDSS_HKFT.h
index 35804760a..a169f97e5 100644
--- a/Cantera/src/thermo/PDSS_HKFT.h
+++ b/Cantera/src/thermo/PDSS_HKFT.h
@@ -431,6 +431,20 @@ namespace Cantera {
     double ag(const double temp, const int ifunc = 0) const;
     double bg(const double temp, const int ifunc = 0) const;
     double g(const double temp, const double pres, const int ifunc = 0) const;
+
+    //! Difference function f appearing in the formulation
+    /*!
+     * Function f appearing in the Johnson et al formulation of omega_j
+     *   Eqn. 33 ref
+     * 
+     * @param temp      Temperature kelvin
+     * @param pres      Pressure (pascal)
+     * @param ifunc     parameters specifying the desired information
+     *                 - 0 function value
+     *                 - 1 derivative wrt temperature
+     *                 - 2 2nd derivative wrt temperature
+     *                 - 3 derivative wrt pressure
+     */
     double f(const double temp, const double pres, const int ifunc = 0) const;
     double gstar(const double temp, const double pres, const int ifunc = 0) const;
 
diff --git a/Cantera/src/thermo/PDSS_Water.cpp b/Cantera/src/thermo/PDSS_Water.cpp
index 0bc11c0ed..477e20e53 100644
--- a/Cantera/src/thermo/PDSS_Water.cpp
+++ b/Cantera/src/thermo/PDSS_Water.cpp
@@ -449,7 +449,12 @@ namespace Cantera {
     doublereal val = (val2 - vald) / 0.04;
     return val; 
   }
-  
+   
+  doublereal PDSS_Water::isothermalCompressibility() const {
+    doublereal pres = pressure();
+    doublereal val = m_sub->isothermalCompressibility(m_temp, pres);
+    return val; 
+  }
 
   /// critical temperature 
   doublereal PDSS_Water::critTemperature() const { return m_sub->Tcrit(); }
@@ -480,7 +485,7 @@ namespace Cantera {
     setPressure(pres);
   }
 
-  /// saturation pressure
+  // saturation pressure
   doublereal PDSS_Water::satPressure(doublereal t){
     doublereal pp = m_sub->psat(t);
     doublereal dens = m_dens;
diff --git a/Cantera/src/thermo/PDSS_Water.h b/Cantera/src/thermo/PDSS_Water.h
index 90734d398..1607b61e7 100644
--- a/Cantera/src/thermo/PDSS_Water.h
+++ b/Cantera/src/thermo/PDSS_Water.h
@@ -335,6 +335,19 @@ namespace Cantera {
      */
     virtual doublereal dthermalExpansionCoeffdT() const;
 
+    //! Returns  the isothermal compressibility. Units: 1/Pa.
+    /*!
+     * The isothermal compressibility is defined as
+     * \f[
+     * \kappa_T = -\frac{1}{v}\left(\frac{\partial v}{\partial P}\right)_T
+     * \f]
+     *  or
+     * \f[
+     * \kappa_T = \frac{1}{\rho}\left(\frac{\partial \rho}{\partial P}\right)_T
+     * \f]
+     */
+    virtual doublereal isothermalCompressibility() const;
+
     /**
      * @}
      *  @name  Miscellaneous properties of the standard state
diff --git a/Cantera/src/thermo/ThermoPhase.h b/Cantera/src/thermo/ThermoPhase.h
index 7679e18cd..eb1a8ac8d 100755
--- a/Cantera/src/thermo/ThermoPhase.h
+++ b/Cantera/src/thermo/ThermoPhase.h
@@ -873,6 +873,10 @@ namespace Cantera {
      * \f[
      * \kappa_T = -\frac{1}{v}\left(\frac{\partial v}{\partial P}\right)_T
      * \f]
+     *  or
+     * \f[
+     * \kappa_T = \frac{1}{\rho}\left(\frac{\partial \rho}{\partial P}\right)_T
+     * \f]
      */
     virtual doublereal isothermalCompressibility() const {
       err("isothermalCompressibility"); return -1.0;
diff --git a/Cantera/src/thermo/WaterSSTP.cpp b/Cantera/src/thermo/WaterSSTP.cpp
index 72db00445..dc052a78b 100644
--- a/Cantera/src/thermo/WaterSSTP.cpp
+++ b/Cantera/src/thermo/WaterSSTP.cpp
@@ -513,7 +513,18 @@ namespace Cantera {
     doublereal val = m_sub->coeffThermExp(T, pres);
     return val;
   }
- 
+
+  doublereal WaterSSTP::dthermalExpansionCoeffdT() const {
+    doublereal pres = pressure();
+    double T = temperature();
+    double tt = T - 0.04;
+    doublereal vald = m_sub->coeffThermExp(tt, pres);
+    doublereal val2 = m_sub->coeffThermExp(T, pres);
+    doublereal val = (val2 - vald) / 0.04;
+    return val;
+  }
+
+
   // critical temperature 
   doublereal WaterSSTP::critTemperature() const { return m_sub->Tcrit(); }
         
diff --git a/Cantera/src/thermo/WaterSSTP.h b/Cantera/src/thermo/WaterSSTP.h
index c2fcbb597..2df13b6e7 100644
--- a/Cantera/src/thermo/WaterSSTP.h
+++ b/Cantera/src/thermo/WaterSSTP.h
@@ -195,7 +195,15 @@ namespace Cantera {
      */
     virtual doublereal thermalExpansionCoeff() const;
  
-
+    //! Return the derivative of the volumetric thermal expansion coefficient. Units: 1/K2.
+    /*!
+     * The thermal expansion coefficient is defined as
+     * \f[
+     * \beta = \frac{1}{v}\left(\frac{\partial v}{\partial T}\right)_P
+     * \f]
+     */
+    virtual doublereal dthermalExpansionCoeffdT() const;
+    
     /**
      * @} 
      * @name Potential Energy