diff --git a/Source/fire.f90 b/Source/fire.f90
index 1d698f8ec2d..c8619182272 100644
--- a/Source/fire.f90
+++ b/Source/fire.f90
@@ -1186,73 +1186,83 @@ SUBROUTINE CALC_AFT_REAC_AND_PROD(ZZ,ZZ_REAC,ZZ_PROD)
 
 REAL(EB), INTENT(IN) :: ZZ(N_TRACKED_SPECIES)
 REAL(EB), INTENT(OUT) :: ZZ_REAC(N_TRACKED_SPECIES),ZZ_PROD(N_TRACKED_SPECIES)
+REAL(EB) :: ZZ_EQUIV(N_TRACKED_SPECIES)
 REAL(EB) :: EQUIV, X,Y,Z,A,B,C,D,E, SUM_ZZ
 REAL(EB) :: ZZ_MASS, ZZ_FUEL_O2_MASS
 REAL(EB) :: REAC_MASS, PROD_MASS, FUEL_MASS, O2_MASS, CO2_MASS, H2O_MASS
 INTEGER :: NS
-
-CALL CALC_EQUIV_RATIO(ZZ(1:N_TRACKED_SPECIES), EQUIV)
-IF (SIM_MODE /= DNS_MODE .AND. USE_MIXED_ZN_AFT_TMP) THEN
-   EQUIV = MAX(1._EB,EQUIV)
-ENDIF
+REAL(EB), PARAMETER:: EQUIV_TOL=1.E-4_EB
 
 ! Adjust for diluents
 ZZ_FUEL_O2_MASS = 0._EB
 ZZ_MASS = SUM(ZZ(1:N_TRACKED_SPECIES))
+ZZ_EQUIV = 0.0_EB
 ZZ_REAC(1:N_TRACKED_SPECIES) = ZZ(1:N_TRACKED_SPECIES)
 ZZ_PROD(1:N_TRACKED_SPECIES) = ZZ(1:N_TRACKED_SPECIES)
 DO NS=1, N_TRACKED_SPECIES
-   IF (SPECIES_MIXTURE(NS)%OXR > TWO_EPSILON_EB) THEN ! FUEL
+   IF (SPECIES_MIXTURE(NS)%OXR > TWO_EPSILON_EB .AND. &
+          ABS(SPECIES_MIXTURE(NS)%EQUIV - 1.0_EB) > EQUIV_TOL) THEN ! FUEL
       ZZ_REAC(NS) = 0._EB
       ZZ_PROD(NS) = 0._EB
       ZZ_FUEL_O2_MASS = ZZ_FUEL_O2_MASS + ZZ(NS)
+      ZZ_EQUIV(NS) = ZZ(NS)
    ENDIF   
 ENDDO
 ZZ_REAC(I_O2) = 0._EB
 ZZ_PROD(I_O2) = 0._EB
+ZZ_EQUIV(I_O2) = ZZ(I_O2)
 ZZ_FUEL_O2_MASS = ZZ_FUEL_O2_MASS + ZZ(I_O2)
 
-! Based on CxHyOz + aO2 = bCO2 + cH2O + dCxHyOz + eO2 
-X=SPECIES_MIXTURE(I_FUEL)%ATOMS(6) !C
-Y=SPECIES_MIXTURE(I_FUEL)%ATOMS(1) !H
-Z=SPECIES_MIXTURE(I_FUEL)%ATOMS(8) !O
-A=0.5_EB*((2._EB*X+0.5_EB*Y)/EQUIV -Z) ! a is a function of equivalence ratio
-IF (ABS(EQUIV - 1.0_EB) < TWO_EPSILON_EB) THEN ! Stoich
-   B = X
-   C = 0.5_EB*Y
-   D = 0._EB ! No fuel
-   E = 0._EB ! No O2
-ELSEIF (EQUIV > 1) THEN ! Rich
-   D = (2._EB*X+0.5_EB*Y-2._EB*A-Z)/(2._EB*X+0.5_EB*Y-Z)
-   B = (1._EB-D)*X
-   C = 0.5_EB*(1._EB-D)*Y
-   E = 0._EB ! No O2
-ELSE !EQUIV < 1, Lean
-   B = X
-   C = 0.5_EB*Y
-   D = 0._EB ! No fuel
-   E = A + 0.5*Z - B - 0.5_EB*C
-ENDIF
+IF (ZZ_FUEL_O2_MASS > TWO_EPSILON_EB) THEN
+   SUM_ZZ=SUM(ZZ_EQUIV)
+   ZZ_EQUIV = ZZ_EQUIV/(SUM_ZZ + TWO_EPSILON_EB)
+   CALL CALC_EQUIV_RATIO(ZZ_EQUIV(1:N_TRACKED_SPECIES), EQUIV)
+   IF (SIM_MODE /= DNS_MODE .AND. USE_MIXED_ZN_AFT_TMP) THEN
+      EQUIV = MAX(1._EB,EQUIV)
+   ENDIF
 
-! Setup reactants
-FUEL_MASS = 1._EB*SPECIES_MIXTURE(I_FUEL)%MW
-O2_MASS = A*SPECIES_MIXTURE(I_O2)%MW
-REAC_MASS = FUEL_MASS+O2_MASS
-ZZ_REAC(I_FUEL)=FUEL_MASS/REAC_MASS*ZZ_FUEL_O2_MASS
-ZZ_REAC(I_O2)=O2_MASS/REAC_MASS*ZZ_FUEL_O2_MASS
-SUM_ZZ=SUM(ZZ_REAC)
-ZZ_REAC = ZZ_REAC/SUM_ZZ
-
-! Setup products
-CO2_MASS = B*SPECIES_MIXTURE(I_CO2)%MW
-H2O_MASS = C*SPECIES_MIXTURE(I_H2O)%MW
-FUEL_MASS = D*SPECIES_MIXTURE(I_FUEL)%MW
-O2_MASS = E*SPECIES_MIXTURE(I_O2)%MW
-PROD_MASS = CO2_MASS+H2O_MASS+FUEL_MASS+O2_MASS
-ZZ_PROD(I_CO2)=ZZ_PROD(I_CO2)+CO2_MASS/PROD_MASS*ZZ_FUEL_O2_MASS
-ZZ_PROD(I_H2O)=ZZ_PROD(I_H2O)+H2O_MASS/PROD_MASS*ZZ_FUEL_O2_MASS
-ZZ_PROD(I_FUEL)=FUEL_MASS/PROD_MASS*ZZ_FUEL_O2_MASS
-ZZ_PROD(I_O2)=O2_MASS/PROD_MASS*ZZ_FUEL_O2_MASS
+   ! Based on CxHyOz + aO2 = bCO2 + cH2O + dCxHyOz + eO2 
+   X=SPECIES_MIXTURE(I_FUEL)%ATOMS(6) !C
+   Y=SPECIES_MIXTURE(I_FUEL)%ATOMS(1) !H
+   Z=SPECIES_MIXTURE(I_FUEL)%ATOMS(8) !O
+   A=0.5_EB*((2._EB*X+0.5_EB*Y)/EQUIV -Z) ! a is a function of equivalence ratio
+   IF (ABS(EQUIV - 1.0_EB) < EQUIV_TOL) THEN ! Stoich
+      B = X
+      C = 0.5_EB*Y
+      D = 0._EB ! No fuel
+      E = 0._EB ! No O2
+   ELSEIF (EQUIV > 1) THEN ! Rich
+      D = (2._EB*X+0.5_EB*Y-2._EB*A-Z)/(2._EB*X+0.5_EB*Y-Z)
+      B = (1._EB-D)*X
+      C = 0.5_EB*(1._EB-D)*Y
+      E = 0._EB ! No O2
+   ELSE !EQUIV < 1, Lean
+      B = X
+      C = 0.5_EB*Y
+      D = 0._EB ! No fuel
+      E = A + 0.5*Z - B - 0.5_EB*C
+   ENDIF
+
+   ! Setup reactants
+   FUEL_MASS = 1._EB*SPECIES_MIXTURE(I_FUEL)%MW
+   O2_MASS = A*SPECIES_MIXTURE(I_O2)%MW
+   REAC_MASS = FUEL_MASS+O2_MASS
+   ZZ_REAC(I_FUEL)=FUEL_MASS/REAC_MASS*ZZ_FUEL_O2_MASS
+   ZZ_REAC(I_O2)=O2_MASS/REAC_MASS*ZZ_FUEL_O2_MASS
+   SUM_ZZ=SUM(ZZ_REAC)
+   ZZ_REAC = ZZ_REAC/SUM_ZZ
+
+   ! Setup products
+   CO2_MASS = B*SPECIES_MIXTURE(I_CO2)%MW
+   H2O_MASS = C*SPECIES_MIXTURE(I_H2O)%MW
+   FUEL_MASS = D*SPECIES_MIXTURE(I_FUEL)%MW
+   O2_MASS = E*SPECIES_MIXTURE(I_O2)%MW
+   PROD_MASS = CO2_MASS+H2O_MASS+FUEL_MASS+O2_MASS
+   ZZ_PROD(I_CO2)=ZZ_PROD(I_CO2)+CO2_MASS/PROD_MASS*ZZ_FUEL_O2_MASS
+   ZZ_PROD(I_H2O)=ZZ_PROD(I_H2O)+H2O_MASS/PROD_MASS*ZZ_FUEL_O2_MASS
+   ZZ_PROD(I_FUEL)=FUEL_MASS/PROD_MASS*ZZ_FUEL_O2_MASS
+   ZZ_PROD(I_O2)=O2_MASS/PROD_MASS*ZZ_FUEL_O2_MASS
+ENDIF
 SUM_ZZ=SUM(ZZ_PROD)
 ZZ_PROD = ZZ_PROD/SUM_ZZ
 
diff --git a/Source/read.f90 b/Source/read.f90
index 5df87474b63..0ea195441c1 100644
--- a/Source/read.f90
+++ b/Source/read.f90
@@ -3458,6 +3458,7 @@ SUBROUTINE READ_SPEC
                                 * ELEMENT(8)%MASS / SPECIES_MIXTURE(N1)%MW
 
    SPECIES_MIXTURE(N1)%OXA = SPECIES_MIXTURE(N1)%ATOMS(8) * ELEMENT(8)%MASS / SPECIES_MIXTURE(N1)%MW
+   SPECIES_MIXTURE(N1)%EQUIV = SPECIES_MIXTURE(N1)%OXR/(SPECIES_MIXTURE(N1)%OXA+TWO_EPSILON_EB)
 ENDDO
 
 !If SOOT_OXIDATION is enabled make sure to save accumulation on the wall and check that it is an AEROSOL species
diff --git a/Source/type.f90 b/Source/type.f90
index 1e3d3f6ba98..a6e438c9d09 100644
--- a/Source/type.f90
+++ b/Source/type.f90
@@ -650,6 +650,7 @@ MODULE TYPES
    REAL(EB), ALLOCATABLE, DIMENSION(:) :: R50
    REAL(EB) :: OXR                  !< Required oxygen for complete combustion (gm/gm-species)
    REAL(EB) :: OXA                  !< Available oxygen for combustion (gm/gm-species)
+   REAL(EB) :: EQUIV                !< Species equiv ratio OXR/OXA
 
 
 END TYPE SPECIES_MIXTURE_TYPE