diff --git a/singularity-eos/eos/eos_base.hpp b/singularity-eos/eos/eos_base.hpp
index e107f2ee82..3f97babe09 100644
--- a/singularity-eos/eos/eos_base.hpp
+++ b/singularity-eos/eos/eos_base.hpp
@@ -134,6 +134,23 @@ struct Transform {
   Factor x, y, f;
 };
 
+/*
+  This is a utility struct used for analytic equations of state,
+  allowing them to store/report mean atomic mass/number easily.
+ */
+struct MeanAtomicProperties {
+  Real Abar, Zbar;
+
+  // default is hydrogen
+  static constexpr Real DEFAULT_ABAR = 1.0;
+  static constexpr Real DEFAULT_ZBAR = 1.0;
+
+  PORTABLE_INLINE_FUNCTION
+  MeanAtomicProperties(Real Abar_, Real Zbar_) : Abar(Abar_), Zbar(Zbar_) {}
+  PORTABLE_INLINE_FUNCTION
+  MeanAtomicProperties() : Abar(DEFAULT_ABAR), Zbar(DEFAULT_ZBAR) {}
+};
+
 /*
 This is a CRTP that allows for static inheritance so that default behavior for
 various member functions can be defined.
@@ -751,23 +768,29 @@ class EosBase {
   // developer is in charge of either throwing an error or choosing
   // reasonable defaults.
   PORTABLE_INLINE_FUNCTION
-  Real MeanAtomicMass() const { return 1.0; }
+  Real MeanAtomicMass() const {
+    PORTABLE_THROW_OR_ABORT("Mean atomic mass not implemented!");
+    return 1.0;
+  }
   PORTABLE_INLINE_FUNCTION
-  Real MeanAtomicNumber() const { return 1.0; }
+  Real MeanAtomicNumber() const {
+    PORTABLE_THROW_OR_ABORT("Mean atomic number not implemented!");
+    return 1.0;
+  }
   // TODO(JMM): Should we provide vector implementations if we depend on rho, T, etc?
   template <typename Indexer_t = Real *>
   PORTABLE_INLINE_FUNCTION Real MeanAtomicMassFromDensityTemperature(
       const Real rho, const Real T,
       Indexer_t &&lambda = static_cast<Real *>(nullptr)) const {
     CRTP copy = *(static_cast<CRTP const *>(this));
-    return copy.MeanAtomicMass(rho, T, lambda);
+    return copy.MeanAtomicMass();
   }
   template <typename Indexer_t = Real *>
   PORTABLE_INLINE_FUNCTION Real MeanAtomicNumberFromDensityTemperature(
       const Real rho, const Real T,
       Indexer_t &&lambda = static_cast<Real *>(nullptr)) const {
     CRTP copy = *(static_cast<CRTP const *>(this));
-    return copy.MeanAtomicNumber(rho, T, lambda);
+    return copy.MeanAtomicNumber();
   }
 
   // Default entropy behavior is to cause an error
diff --git a/singularity-eos/eos/eos_ideal.hpp b/singularity-eos/eos/eos_ideal.hpp
index d395928404..ddb17c243f 100644
--- a/singularity-eos/eos/eos_ideal.hpp
+++ b/singularity-eos/eos/eos_ideal.hpp
@@ -38,16 +38,20 @@ using namespace eos_base;
 class IdealGas : public EosBase<IdealGas> {
  public:
   IdealGas() = default;
-  PORTABLE_INLINE_FUNCTION IdealGas(Real gm1, Real Cv)
+  PORTABLE_INLINE_FUNCTION
+  IdealGas(Real gm1, Real Cv, const MeanAtomicProperties &AZbar = MeanAtomicProperties())
       : _Cv(Cv), _gm1(gm1), _rho0(_P0 / (_gm1 * _Cv * _T0)), _sie0(_Cv * _T0),
         _bmod0((_gm1 + 1) * _gm1 * _rho0 * _Cv * _T0), _dpde0(_gm1 * _rho0),
-        _dvdt0(1. / (_rho0 * _T0)), _EntropyT0(_T0), _EntropyRho0(_rho0) {
+        _dvdt0(1. / (_rho0 * _T0)), _EntropyT0(_T0), _EntropyRho0(_rho0), _AZbar(AZbar) {
     CheckParams();
   }
-  PORTABLE_INLINE_FUNCTION IdealGas(Real gm1, Real Cv, Real EntropyT0, Real EntropyRho0)
+  PORTABLE_INLINE_FUNCTION
+  IdealGas(Real gm1, Real Cv, Real EntropyT0, Real EntropyRho0,
+           const MeanAtomicProperties &AZbar = MeanAtomicProperties())
       : _Cv(Cv), _gm1(gm1), _rho0(_P0 / (_gm1 * _Cv * _T0)), _sie0(_Cv * _T0),
         _bmod0((_gm1 + 1) * _gm1 * _rho0 * _Cv * _T0), _dpde0(_gm1 * _rho0),
-        _dvdt0(1. / (_rho0 * _T0)), _EntropyT0(EntropyT0), _EntropyRho0(EntropyRho0) {
+        _dvdt0(1. / (_rho0 * _T0)), _EntropyT0(EntropyT0), _EntropyRho0(EntropyRho0),
+        _AZbar(AZbar) {
     CheckParams();
   }
 
@@ -148,6 +152,12 @@ class IdealGas : public EosBase<IdealGas> {
   FillEos(Real &rho, Real &temp, Real &energy, Real &press, Real &cv, Real &bmod,
           const unsigned long output,
           Indexer_t &&lambda = static_cast<Real *>(nullptr)) const;
+
+  PORTABLE_INLINE_FUNCTION
+  Real MeanAtomicMass() const { return _AZbar.Abar; }
+  PORTABLE_INLINE_FUNCTION
+  Real MeanAtomicNumber() const { return _AZbar.Zbar; }
+
   template <typename Indexer_t = Real *>
   PORTABLE_INLINE_FUNCTION void
   ValuesAtReferenceState(Real &rho, Real &temp, Real &sie, Real &press, Real &cv,
@@ -198,6 +208,8 @@ class IdealGas : public EosBase<IdealGas> {
       thermalqs::density | thermalqs::specific_internal_energy;
   // optional entropy reference state variables
   Real _EntropyT0, _EntropyRho0;
+  // optional mean atomic mass and number
+  MeanAtomicProperties _AZbar;
 };
 
 template <typename Indexer_t>