diff --git a/opm/core/props/phaseUsageFromDeck.hpp b/opm/core/props/phaseUsageFromDeck.hpp
index 01f28ee14..e69d6ee2f 100644
--- a/opm/core/props/phaseUsageFromDeck.hpp
+++ b/opm/core/props/phaseUsageFromDeck.hpp
@@ -24,11 +24,50 @@
 #include <opm/core/io/eclipse/EclipseGridParser.hpp>
 #include <opm/core/props/BlackoilPhases.hpp>
 
+#include <opm/parser/eclipse/EclipseState/EclipseState.hpp>
+
 
 namespace Opm
 {
 
 
+    /// Looks at presence of WATER, OIL and GAS keywords in state object
+    /// to determine active phases.
+    inline PhaseUsage phaseUsageFromDeck(Opm::EclipseStateConstPtr eclipseState)
+    {
+        PhaseUsage pu;
+        std::fill(pu.phase_used, pu.phase_used + BlackoilPhases::MaxNumPhases, 0);
+
+        // Discover phase usage.
+        if (eclipseState->hasPhase(PhaseEnum::WATER)) {
+            pu.phase_used[BlackoilPhases::Aqua] = 1;
+        }
+        if (eclipseState->hasPhase(PhaseEnum::OIL)) {
+            pu.phase_used[BlackoilPhases::Liquid] = 1;
+        }
+        if (eclipseState->hasPhase(PhaseEnum::GAS)) {
+            pu.phase_used[BlackoilPhases::Vapour] = 1;
+        }
+        pu.num_phases = 0;
+        for (int i = 0; i < BlackoilPhases::MaxNumPhases; ++i) {
+            pu.phase_pos[i] = pu.num_phases;
+            pu.num_phases += pu.phase_used[i];
+        }
+
+        // Only 2 or 3 phase systems handled.
+        if (pu.num_phases < 2 || pu.num_phases > 3) {
+            OPM_THROW(std::runtime_error, "Cannot handle cases with " << pu.num_phases << " phases.");
+        }
+
+        // We need oil systems, since we do not support the keywords needed for
+        // water-gas systems.
+        if (!pu.phase_used[BlackoilPhases::Liquid]) {
+            OPM_THROW(std::runtime_error, "Cannot handle cases with no OIL, i.e. water-gas systems.");
+        }
+
+        return pu;
+    }
+
     /// Looks at presence of WATER, OIL and GAS keywords in deck
     /// to determine active phases.
     inline PhaseUsage phaseUsageFromDeck(const EclipseGridParser& deck)
diff --git a/opm/core/wells/WellsManager.cpp b/opm/core/wells/WellsManager.cpp
index 86a7d78dd..46a476465 100644
--- a/opm/core/wells/WellsManager.cpp
+++ b/opm/core/wells/WellsManager.cpp
@@ -261,7 +261,7 @@ namespace Opm
         }
 
         // Obtain phase usage data.
-        PhaseUsage pu = phaseUsageFromDeck(deck);
+        PhaseUsage pu = phaseUsageFromDeck(eclipseState);
 
         // These data structures will be filled in this constructor,
         // then used to initialize the Wells struct.