diff --git a/Cantera/src/thermo/MargulesVPSSTP.cpp b/Cantera/src/thermo/MargulesVPSSTP.cpp
index 216e6a273..708d0e130 100644
--- a/Cantera/src/thermo/MargulesVPSSTP.cpp
+++ b/Cantera/src/thermo/MargulesVPSSTP.cpp
@@ -340,15 +340,40 @@ namespace Cantera {
    * - Activities, Standard States, Activity Concentrations -----------
    */
 
+  // This method returns an array of generalized concentrations
+  /*
+   * \f$ C^a_k\f$ are defined such that \f$ a_k = C^a_k /
+   * C^0_k, \f$ where \f$ C^0_k \f$ is a standard concentration
+   * defined below and \f$ a_k \f$ are activities used in the
+   * thermodynamic functions.  These activity (or generalized)
+   * concentrations are used
+   * by kinetics manager classes to compute the forward and
+   * reverse rates of elementary reactions. Note that they may
+   * or may not have units of concentration --- they might be
+   * partial pressures, mole fractions, or surface coverages,
+   * for example.
+   *
+   *  Here we define the activity concentrations as equal
+   *  to the activities, because the standard concentration is 1.
+   *
+   * @param c Output array of generalized concentrations. The
+   *           units depend upon the implementation of the
+   *           reaction rate expressions within the phase.
+   */
+  void MargulesVPSSTP::getActivityConcentrations(doublereal* c) const {
+    getActivities(c);
+  }
 
   doublereal MargulesVPSSTP::standardConcentration(int k) const {
-    err("standardConcentration");
-    return -1.0;
+    //err("standardConcentration");
+    //return -1.0;
+    return 1.0;
   }
 
   doublereal MargulesVPSSTP::logStandardConc(int k) const {
-    err("logStandardConc");
-    return -1.0;
+    //err("logStandardConc");
+    //return -1.0;
+    return 0.0;
   }
 
   // Get the array of non-dimensional molar-based activity coefficients at
diff --git a/Cantera/src/thermo/MargulesVPSSTP.h b/Cantera/src/thermo/MargulesVPSSTP.h
index 53a57904a..7e92c4a6b 100644
--- a/Cantera/src/thermo/MargulesVPSSTP.h
+++ b/Cantera/src/thermo/MargulesVPSSTP.h
@@ -474,7 +474,24 @@ namespace Cantera {
      * @{
      */
 
-  
+    //! This method returns an array of generalized concentrations
+    /*!
+     * \f$ C^a_k\f$ are defined such that \f$ a_k = C^a_k /
+     * C^0_k, \f$ where \f$ C^0_k \f$ is a standard concentration
+     * defined below and \f$ a_k \f$ are activities used in the
+     * thermodynamic functions.  These activity (or generalized)
+     * concentrations are used
+     * by kinetics manager classes to compute the forward and
+     * reverse rates of elementary reactions. Note that they may
+     * or may not have units of concentration --- they might be
+     * partial pressures, mole fractions, or surface coverages,
+     * for example.
+     *
+     * @param c Output array of generalized concentrations. The
+     *           units depend upon the implementation of the
+     *           reaction rate expressions within the phase.
+     */
+    virtual void getActivityConcentrations(doublereal* c) const; 
  
 
     /**