diff --git a/include/DataStructures.h b/include/DataStructures.h
index 45a4593c..5dc880c7 100644
--- a/include/DataStructures.h
+++ b/include/DataStructures.h
@@ -115,6 +115,7 @@ enum parameters{
     idBvirial_dT, ///< Derivative of second virial coefficient with temperature
     idCvirial_dT, ///< Derivative of third virial coefficient with temperature
     iZ, ///< The compressibility factor Z = p*v/(R*T)
+    iPIP, ///< The phase identification parameter of Venkatarathnam and Oellrich
     
     // Accessors for incompressibles
     ifraction_min, ///< The minimum fraction (mole, mass, volume) for incompressibles
diff --git a/src/AbstractState.cpp b/src/AbstractState.cpp
index 3affc28c..db0fd0ce 100644
--- a/src/AbstractState.cpp
+++ b/src/AbstractState.cpp
@@ -315,6 +315,8 @@ double AbstractState::keyed_output(parameters key)
         return phase();
     case iZ:
         return compressibility_factor();
+    case iPIP:
+        return PIP();
     default:
         throw ValueError(format("This input [%d: \"%s\"] is not valid for keyed_output",key,get_parameter_information(key,"short").c_str()));
     }
diff --git a/src/DataStructures.cpp b/src/DataStructures.cpp
index e706f483..c82a4dc3 100644
--- a/src/DataStructures.cpp
+++ b/src/DataStructures.cpp
@@ -80,6 +80,7 @@ const parameter_info parameter_info_list[] = {
     {iisobaric_expansion_coefficient,         "isobaric_expansion_coefficient",         "O", "1/K",  "Isobaric expansion coefficient",false},
     {iZ,                                      "Z",                                      "O", "-",    "Compressibility factor",false},
     {ifundamental_derivative_of_gas_dynamics, "fundamental_derivative_of_gas_dynamics", "O", "-",    "Fundamental derivative of gas dynamics",false},
+    {iPIP,                                    "PIP",                                    "O", "-",    "Phase identification parameter", false},
     
     {ialphar,                  "alphar",                  "O", "-", "Residual Helmholtz energy", false},
     {idalphar_dtau_constdelta, "dalphar_dtau_constdelta", "O", "-", "Derivative of residual Helmholtz energy with tau",false},