diff --git a/Cantera/src/equil/MultiPhase.cpp b/Cantera/src/equil/MultiPhase.cpp
index 1d4ef9b2c..f746a035d 100644
--- a/Cantera/src/equil/MultiPhase.cpp
+++ b/Cantera/src/equil/MultiPhase.cpp
@@ -322,6 +322,16 @@ namespace Cantera {
         return sum;
     }
 
+  /// The internal energy of the mixture (J).
+  doublereal MultiPhase::IntEnergy() const {
+    index_t i;
+    doublereal sum = 0.0;
+    updatePhases();
+    for (i = 0; i < m_np; i++) 
+      sum += m_phase[i]->intEnergy_mole() * m_moles[i];
+    return sum;
+  }
+
     /// The entropy of the mixture (J/K).
     doublereal MultiPhase::entropy() const {
         index_t i;
diff --git a/Cantera/src/equil/MultiPhase.h b/Cantera/src/equil/MultiPhase.h
index ca9440eab..901059be8 100644
--- a/Cantera/src/equil/MultiPhase.h
+++ b/Cantera/src/equil/MultiPhase.h
@@ -22,17 +22,30 @@ namespace Cantera {
   //! number of phases of any type. 
   /*!
    *    All phases have the same
-   *    temperature and pressure, and a specified number of moles.
+   *    temperature and pressure, and a specified number of moles for
+   *    each phase.
    *    The phases do not need to have the same elements. For example,
    *    a mixture might consist of a gaseous phase with elements (H,
    *    C, O, N), a solid carbon phase containing only element C,
    *    etc. A master element set will be constructed for the mixture
-   *    that is the union of the elements of each phase.
+   *    that is the intersection of the elements of each phase.
+   *
+   *   This object is the basic tool used by Cantera for use in
+   *   Multiphase equilibrium calculations. 
    *
    *   Below, reference is made to global species and global elements.
    *   These refer to the collective species and elements encompassing
    *   all of the phases tracked by the object. 
    *
+   *   The global element list kept by this object is an
+   *   intersection of the element lists of all the phases that
+   *   comprise the MultiPhase.
+   *
+   *   The global species list kept by this object is a
+   *   concatenated list of all of the species in all the phases that
+   *   comprise the MultiPhase. The ordering of species is contiguous
+   *   with respect to the phase id.
+   *
    *  @ingroup equilfunctions
    */
   class MultiPhase {
@@ -333,6 +346,9 @@ namespace Cantera {
     /// Enthalpy [J].
     doublereal enthalpy() const;
 
+    /// Enthalpy [J].
+    doublereal IntEnergy() const;
+
     /// Entropy [J/K].
     doublereal entropy() const;