diff --git a/examples/python/pincell/build-xml.py b/examples/python/pincell/build-xml.py
index 979614d635..2a550b9d73 100644
--- a/examples/python/pincell/build-xml.py
+++ b/examples/python/pincell/build-xml.py
@@ -51,7 +51,7 @@ o = openmc.Element('O')
 # Instantiate some Materials and register the appropriate Nuclides
 uo2 = openmc.Material(material_id=1, name='UO2 fuel at 2.4% wt enrichment')
 uo2.set_density('g/cm3', 10.29769)
-uo2.add_element(u, 1., enrichment=0.024)
+uo2.add_element(u, 1., enrichment=2.4)
 uo2.add_element(o, 2.)
 
 helium = openmc.Material(material_id=2, name='Helium for gap')
diff --git a/openmc/data/data.py b/openmc/data/data.py
index 1f759d3d4d..5dee5aca73 100644
--- a/openmc/data/data.py
+++ b/openmc/data/data.py
@@ -1,5 +1,6 @@
 import itertools
 import os
+import re
 
 
 # Isotopic abundances from M. Berglund and M. E. Wieser, "Isotopic compositions
@@ -149,6 +150,28 @@ def atomic_mass(isotope):
 
     """
     if not _ATOMIC_MASS:
+
+        # If the isotope represents all natural isotopes of the element
+        # (e.g. C0), set atomic mass manually using the values from Atomic
+        # weights of the elements 2013 (IUPAC Technical Report)
+        # (doi:10.1515/pac-2015-0305). In cases where an atomic mass range is
+        # given (e.g. C), the average value is used.
+        if int(re.split(r"(\d+)", isotope)[1]) == 0:
+            if re.split(r"(\d+)", isotope)[0] == 'C':
+                _ATOMIC_MASS[isotope.lower()] = 12.0106
+            elif re.split(r"(\d+)", isotope)[0] == 'Zn':
+                _ATOMIC_MASS[isotope.lower()] = 65.38
+            elif re.split(r"(\d+)", isotope)[0] == 'Pt':
+                _ATOMIC_MASS[isotope.lower()] = 195.084
+            elif re.split(r"(\d+)", isotope)[0] == 'Os':
+                _ATOMIC_MASS[isotope.lower()] = 190.23
+            elif re.split(r"(\d+)", isotope)[0] == 'Tl':
+                _ATOMIC_MASS[isotope.lower()] = 204.3835
+            else:
+                msg = 'Could not get the atomic mass for zero isotope'\
+                      ' {0}.'.format(isotope)
+                raise ValueError(msg)
+
         # Load data from AME2012 file
         mass_file = os.path.join(os.path.dirname(__file__), 'mass.mas12')
         with open(mass_file, 'r') as ame:
diff --git a/openmc/element.py b/openmc/element.py
index d56c3b3507..ce0b5e4386 100644
--- a/openmc/element.py
+++ b/openmc/element.py
@@ -233,7 +233,7 @@ class Element(object):
 
         # Compute the ratio of the nuclide atomic masses to the element
         # atomic mass
-        if percent_type == 'wo':
+        if percent_type == 'wo' and len(abundances) > 1:
 
             # Compute the element atomic mass
             element_am = 0.
diff --git a/openmc/material.py b/openmc/material.py
index c265c90694..abd5467b81 100644
--- a/openmc/material.py
+++ b/openmc/material.py
@@ -4,6 +4,7 @@ from numbers import Real, Integral
 import warnings
 from xml.etree import ElementTree as ET
 import sys
+import re
 
 from six import string_types
 
@@ -581,6 +582,33 @@ class Material(object):
 
         return nuclides
 
+    def get_molar_mass(self):
+        """Returns the molar mass of the material
+
+        Returns
+        -------
+        molar_mass : float
+            The molar mass of the material
+
+        """
+
+        # Get a list of all the nuclides, with elements expanded
+        nuclide_densities = self.get_nuclide_densities()
+
+        # Using the sum of specified atomic or weight amounts as a basis, sum
+        # the mass and moles of the material
+        mass = 0.
+        moles = 0.
+        for nuc,vals in nuclide_densities.items():
+            if vals[2] == 'ao':
+                mass += vals[1] * openmc.data.atomic_mass(nuc)
+                moles += vals[1]
+            else:
+                moles += vals[1] / openmc.data.atomic_mass(nuc)
+                mass += vals[1]
+
+        return (mass / moles)
+
     def _get_nuclide_xml(self, nuclide, distrib=False):
         xml_element = ET.Element("nuclide")
         xml_element.set("name", nuclide[0].name)