diff --git a/ApplicationLibCode/ReservoirDataModel/RigActiveCellInfo.cpp b/ApplicationLibCode/ReservoirDataModel/RigActiveCellInfo.cpp
index 3ffae1ccea..2ecf32f6c7 100644
--- a/ApplicationLibCode/ReservoirDataModel/RigActiveCellInfo.cpp
+++ b/ApplicationLibCode/ReservoirDataModel/RigActiveCellInfo.cpp
@@ -81,6 +81,14 @@ void RigActiveCellInfo::setCellResultIndex( size_t reservoirCellIndex, size_t re
     m_cellIndexToResultIndex[reservoirCellIndex] = reservoirCellResultIndex;
 }
 
+//--------------------------------------------------------------------------------------------------
+///
+//--------------------------------------------------------------------------------------------------
+std::vector<size_t> RigActiveCellInfo::activeReservoirCellIndices() const
+{
+    return m_activeCellIndices;
+}
+
 //--------------------------------------------------------------------------------------------------
 ///
 //--------------------------------------------------------------------------------------------------
@@ -110,6 +118,14 @@ void RigActiveCellInfo::computeDerivedData()
     {
         m_reservoirActiveCellCount += m_perGridActiveCellInfo[i].activeCellCount();
     }
+
+    for ( size_t i = 0; i < m_cellIndexToResultIndex.size(); i++ )
+    {
+        if ( m_cellIndexToResultIndex[i] != cvf::UNDEFINED_SIZE_T )
+        {
+            m_activeCellIndices.push_back( i );
+        }
+    }
 }
 
 //--------------------------------------------------------------------------------------------------
diff --git a/ApplicationLibCode/ReservoirDataModel/RigActiveCellInfo.h b/ApplicationLibCode/ReservoirDataModel/RigActiveCellInfo.h
index 3489cfc0a1..f016e2c2dd 100644
--- a/ApplicationLibCode/ReservoirDataModel/RigActiveCellInfo.h
+++ b/ApplicationLibCode/ReservoirDataModel/RigActiveCellInfo.h
@@ -35,9 +35,10 @@ public:
     size_t reservoirCellCount() const;
     size_t reservoirActiveCellCount() const;
 
-    bool   isActive( size_t reservoirCellIndex ) const;
-    size_t cellResultIndex( size_t reservoirCellIndex ) const;
-    void   setCellResultIndex( size_t reservoirCellIndex, size_t globalResultCellIndex );
+    bool                isActive( size_t reservoirCellIndex ) const;
+    size_t              cellResultIndex( size_t reservoirCellIndex ) const;
+    void                setCellResultIndex( size_t reservoirCellIndex, size_t globalResultCellIndex );
+    std::vector<size_t> activeReservoirCellIndices() const;
 
     void   setGridCount( size_t gridCount );
     void   setGridActiveCellCounts( size_t gridIndex, size_t activeCellCount );
@@ -71,6 +72,7 @@ private:
     std::vector<GridActiveCellCounts> m_perGridActiveCellInfo;
 
     std::vector<size_t> m_cellIndexToResultIndex;
+    std::vector<size_t> m_activeCellIndices;
 
     size_t m_reservoirActiveCellCount;