diff --git a/opm/core/pressure/CompressibleTpfa.hpp b/opm/core/pressure/CompressibleTpfa.hpp
index 054ac2e4f..0b54178e6 100644
--- a/opm/core/pressure/CompressibleTpfa.hpp
+++ b/opm/core/pressure/CompressibleTpfa.hpp
@@ -90,16 +90,15 @@ namespace Opm
         bool singularPressure() const;
 
     private:
-        void computePerSolveDynamicData(const double dt,
-                                        const BlackoilState& state,
-                                        const WellState& well_state);
-        void computeWellPotentials(const BlackoilState& state);
+        virtual void computePerSolveDynamicData(const double dt,
+                                                const BlackoilState& state,
+                                                const WellState& well_state);
         void computePerIterationDynamicData(const double dt,
                                             const BlackoilState& state,
                                             const WellState& well_state);
-        void computeCellDynamicData(const double dt,
-                                    const BlackoilState& state,
-                                    const WellState& well_state);
+        virtual void computeCellDynamicData(const double dt,
+                                            const BlackoilState& state,
+                                            const WellState& well_state);
         void computeFaceDynamicData(const double dt,
                                     const BlackoilState& state,
                                     const WellState& well_state);
@@ -114,6 +113,8 @@ namespace Opm
         double incrementNorm() const;
         void computeResults(BlackoilState& state,
                             WellState& well_state) const;
+    protected:
+        void computeWellPotentials(const BlackoilState& state);
 
         // ------ Data that will remain unmodified after construction. ------
         const UnstructuredGrid& grid_;
diff --git a/opm/core/transport/reorder/TransportModelCompressibleTwophase.cpp b/opm/core/transport/reorder/TransportModelCompressibleTwophase.cpp
index 697f94a57..01882053b 100644
--- a/opm/core/transport/reorder/TransportModelCompressibleTwophase.cpp
+++ b/opm/core/transport/reorder/TransportModelCompressibleTwophase.cpp
@@ -124,7 +124,7 @@ namespace Opm
     //
     // [[ incompressible was: r(s) = s - s0 + dt/pv*( influx + outflux*f(s) ) ]]
     //
-    //     r(s) = s - B*z0 + dt/pv*( influx + outflux*f(s) )
+    //     r(s) = s - B*z0 + s*(poro - poro0)/poro0 + dt/pv*( influx + outflux*f(s) )
     //
     // @@@ What about the source term
     //
diff --git a/opm/core/utility/miscUtilities.cpp b/opm/core/utility/miscUtilities.cpp
index 16c59b17e..ac9552dc3 100644
--- a/opm/core/utility/miscUtilities.cpp
+++ b/opm/core/utility/miscUtilities.cpp
@@ -70,6 +70,25 @@ namespace Opm
         }
     }
 
+    /// @brief Computes porosity of all cells in a grid, with rock compressibility effects.
+    /// @param[in]  grid               a grid
+    /// @param[in]  porosity_standard  array of grid.number_of_cells porosity values (at standard conditions)
+    /// @param[in]  rock_comp          rock compressibility properties
+    /// @param[in]  pressure           pressure by cell
+    /// @param[out] porosity           porosity (at reservoir condition)
+    void computePorosity(const UnstructuredGrid& grid,
+                         const double* porosity_standard,
+                         const RockCompressibility& rock_comp,
+                         const std::vector<double>& pressure,
+                         std::vector<double>& porosity)
+    {
+        int num_cells = grid.number_of_cells;
+        porosity.resize(num_cells);
+        for (int i = 0; i < num_cells; ++i) {
+            porosity[i] = porosity_standard[i]*rock_comp.poroMult(pressure[i]);
+        }
+    }
+
 
     /// @brief Computes total saturated volumes over all grid cells.
     /// @param[in]  pv        the pore volume by cell.
diff --git a/opm/core/utility/miscUtilities.hpp b/opm/core/utility/miscUtilities.hpp
index 37b252bc2..2def319a9 100644
--- a/opm/core/utility/miscUtilities.hpp
+++ b/opm/core/utility/miscUtilities.hpp
@@ -44,7 +44,7 @@ namespace Opm
 
     /// @brief Computes pore volume of all cells in a grid, with rock compressibility effects.
     /// @param[in]  grid      a grid
-    /// @param[in]  porosity  array of grid.number_of_cells porosity values
+    /// @param[in]  porosity  array of grid.number_of_cells porosity values (at reference pressure)
     /// @param[in]  rock_comp rock compressibility properties
     /// @param[in]  pressure  pressure by cell
     /// @param[out] porevol   the pore volume by cell.
@@ -54,6 +54,17 @@ namespace Opm
                            const std::vector<double>& pressure,
                            std::vector<double>& porevol);
 
+    /// @brief Computes porosity of all cells in a grid, with rock compressibility effects.
+    /// @param[in]  grid               a grid
+    /// @param[in]  porosity_standard  array of grid.number_of_cells porosity values (at reference presure)
+    /// @param[in]  rock_comp          rock compressibility properties
+    /// @param[in]  pressure           pressure by cell
+    /// @param[out] porosity           porosity (at reservoir condition)
+    void computePorosity(const UnstructuredGrid& grid,
+                         const double* porosity_standard,
+                         const RockCompressibility& rock_comp,
+                         const std::vector<double>& pressure,
+                         std::vector<double>& porosity);
 
     /// @brief Computes total saturated volumes over all grid cells.
     /// @param[in]  pv        the pore volume by cell.