diff --git a/src/thermophysicalModels/specie/transport/const/constTransport.H b/src/thermophysicalModels/specie/transport/const/constTransport.H
index 1c85445ac..a19d9809c 100644
--- a/src/thermophysicalModels/specie/transport/const/constTransport.H
+++ b/src/thermophysicalModels/specie/transport/const/constTransport.H
@@ -143,10 +143,13 @@ public:
 
     // Member operators
 
-        inline constTransport& operator=
-        (
-            const constTransport&
-        );
+        inline constTransport& operator=(const constTransport&);
+
+        inline void operator+=(const constTransport&);
+
+        inline void operator-=(const constTransport&);
+
+        inline void operator*=(const scalar);
 
 
     // Friend operators
diff --git a/src/thermophysicalModels/specie/transport/const/constTransportI.H b/src/thermophysicalModels/specie/transport/const/constTransportI.H
index 690b85072..2f45f02bc 100644
--- a/src/thermophysicalModels/specie/transport/const/constTransportI.H
+++ b/src/thermophysicalModels/specie/transport/const/constTransportI.H
@@ -134,6 +134,52 @@ inline constTransport<thermo>& constTransport<thermo>::operator=
 }
 
 
+template<class thermo>
+inline void Foam::constTransport<thermo>::operator+=
+(
+    const constTransport<thermo>& st
+)
+{
+    scalar molr1 = this->nMoles();
+
+    thermo::operator+=(st);
+
+    molr1 /= this->nMoles();
+    scalar molr2 = st.nMoles()/this->nMoles();
+
+    Mu = molr1*Mu + molr2*st.Mu;
+    rPr = 1.0/(molr1/rPr + molr2/st.rPr);
+}
+
+
+template<class thermo>
+inline void Foam::constTransport<thermo>::operator-=
+(
+    const constTransport<thermo>& st
+)
+{
+    scalar molr1 = this->nMoles();
+
+    thermo::operator-=(st);
+
+    molr1 /= this->nMoles();
+    scalar molr2 = st.nMoles()/this->nMoles();
+
+    Mu = molr1*Mu - molr2*st.Mu;
+    rPr = 1.0/(molr1/rPr - molr2/st.rPr);
+}
+
+
+template<class thermo>
+inline void Foam::constTransport<thermo>::operator*=
+(
+    const scalar s
+)
+{
+    thermo::operator*=(s);
+}
+
+
 // * * * * * * * * * * * * * * * Friend Operators  * * * * * * * * * * * * * //
 
 template<class thermo>
diff --git a/src/thermophysicalModels/specie/transport/sutherland/sutherlandTransport.H b/src/thermophysicalModels/specie/transport/sutherland/sutherlandTransport.H
index 5a134d208..9cc9d0c09 100644
--- a/src/thermophysicalModels/specie/transport/sutherland/sutherlandTransport.H
+++ b/src/thermophysicalModels/specie/transport/sutherland/sutherlandTransport.H
@@ -165,10 +165,13 @@ public:
 
     // Member operators
 
-        inline sutherlandTransport& operator=
-        (
-            const sutherlandTransport&
-        );
+        inline sutherlandTransport& operator=(const sutherlandTransport&);
+
+        inline void operator+=(const sutherlandTransport&);
+
+        inline void operator-=(const sutherlandTransport&);
+
+        inline void operator*=(const scalar);
 
 
     // Friend operators
diff --git a/src/thermophysicalModels/specie/transport/sutherland/sutherlandTransportI.H b/src/thermophysicalModels/specie/transport/sutherland/sutherlandTransportI.H
index 576e1229a..241605991 100644
--- a/src/thermophysicalModels/specie/transport/sutherland/sutherlandTransportI.H
+++ b/src/thermophysicalModels/specie/transport/sutherland/sutherlandTransportI.H
@@ -173,6 +173,52 @@ inline sutherlandTransport<thermo>& sutherlandTransport<thermo>::operator=
 }
 
 
+template<class thermo>
+inline void Foam::sutherlandTransport<thermo>::operator+=
+(
+    const sutherlandTransport<thermo>& st
+)
+{
+    scalar molr1 = this->nMoles();
+
+    thermo::operator+=(st);
+
+    molr1 /= this->nMoles();
+    scalar molr2 = st.nMoles()/this->nMoles();
+
+    As = molr1*As + molr2*st.As;
+    Ts = molr1*Ts + molr2*st.Ts;
+}
+
+
+template<class thermo>
+inline void Foam::sutherlandTransport<thermo>::operator-=
+(
+    const sutherlandTransport<thermo>& st
+)
+{
+    scalar molr1 = this->nMoles();
+
+    thermo::operator-=(st);
+
+    molr1 /= this->nMoles();
+    scalar molr2 = st.nMoles()/this->nMoles();
+
+    As = molr1*As - molr2*st.As;
+    Ts = molr1*Ts - molr2*st.Ts;
+}
+
+
+template<class thermo>
+inline void Foam::sutherlandTransport<thermo>::operator*=
+(
+    const scalar s
+)
+{
+    thermo::operator*=(s);
+}
+
+
 // * * * * * * * * * * * * * * * Friend Operators  * * * * * * * * * * * * * //
 
 template<class thermo>