diff --git a/csg2csg/Input.py b/csg2csg/Input.py
index 9a236c6..620642b 100644
--- a/csg2csg/Input.py
+++ b/csg2csg/Input.py
@@ -10,9 +10,10 @@ class InputDeck:
     """ Constructor
     """
 
-    def __init__(self, filename, quick=False):
+    def __init__(self, filename, quick=False, preserve_xsid=False):
         self.filename = filename
         self.quick_process = quick
+        self.preserve_xsid = preserve_xsid
 
         self.file_lines = ""
         self.title = ""
@@ -72,6 +73,7 @@ def get_cell_with_id(self, id):
     # instanciate from input
     def from_input(self, InputDeckClass):
         self.filename = InputDeckClass.filename
+        self.preserve_xsid = InputDeckClass.preserve_xsid
         self.title = InputDeckClass.title
         self.cell_list = InputDeckClass.cell_list
         self.surface_list = InputDeckClass.surface_list
diff --git a/csg2csg/MCNPInput.py b/csg2csg/MCNPInput.py
index 142923f..49329ec 100644
--- a/csg2csg/MCNPInput.py
+++ b/csg2csg/MCNPInput.py
@@ -30,11 +30,11 @@
 class MCNPInput(InputDeck):
     """MCNPInputDeck class - does the actuall processing"""
 
-    preserve_xsid = False
+    # preserve_xsid = False
 
     # constructor
-    def __init__(self, filename="", quick=False):
-        InputDeck.__init__(self, filename, quick)
+    def __init__(self, filename="", quick=False, preserve_xsid=False):
+        InputDeck.__init__(self, filename, quick, preserve_xsid)
 
     #        self.process()
 
diff --git a/csg2csg/SerpentInput.py b/csg2csg/SerpentInput.py
index 3075014..4f58035 100644
--- a/csg2csg/SerpentInput.py
+++ b/csg2csg/SerpentInput.py
@@ -13,8 +13,8 @@ class SerpentInput(InputDeck):
     """SerpentInput class - does the actual processing"""
 
     # constructor
-    def __init__(self, filename=""):
-        InputDeck.__init__(self, filename)
+    def __init__(self, filename="", preserve_xsid=False):
+        InputDeck.__init__(self, filename, preserve_xsid)
 
     # extract a material card from the start line until
     def __get_material_card(self, start_line, mat_num):
@@ -118,7 +118,9 @@ def __write_serpent_surfaces(self, filestream):
     def __write_serpent_materials(self, filestream):
         filestream.write("% --- material definitions --- %\n")
         for material in self.material_list:
-            write_serpent_material(filestream, self.material_list[material])
+            write_serpent_material(
+                filestream, self.material_list[material], self.preserve_xsid
+            )
         return
 
     # main write serpent method, depending upon where the geometry
diff --git a/csg2csg/SerpentMaterialCard.py b/csg2csg/SerpentMaterialCard.py
index ad05104..a7cb075 100644
--- a/csg2csg/SerpentMaterialCard.py
+++ b/csg2csg/SerpentMaterialCard.py
@@ -4,7 +4,7 @@
 from csg2csg.MCNPFormatter import get_fortran_formatted_number
 
 # write a specific serpent material card
-def write_serpent_material(filestream, material):
+def write_serpent_material(filestream, material, preserve_xs):
 
     string = "% " + material.material_name + "\n"
     string += "mat " + str(material.material_number) + " "
@@ -17,7 +17,12 @@ def write_serpent_material(filestream, material):
         string += "\n"
 
     for nuc in material.composition_dictionary:
-        string += "{} {:e} \n".format(nuc, material.composition_dictionary[nuc])
+        if preserve_xs:
+            string += "{}.{} {:e} \n".format(
+                nuc, material.xsid_dictionary[nuc], material.composition_dictionary[nuc]
+            )
+        else:
+            string += "{} {:e} \n".format(nuc, material.composition_dictionary[nuc])
     filestream.write(string)
     return
 
diff --git a/csg2csg/__main__.py b/csg2csg/__main__.py
index 2fa8d90..7dcafa9 100755
--- a/csg2csg/__main__.py
+++ b/csg2csg/__main__.py
@@ -59,6 +59,13 @@ def main():
         action="store_true",
     )
 
+    parser.add_argument(
+        "-xs",
+        "--preserve_xsid",
+        help="Retain xs library for materials",
+        action="store_true",
+    )
+
     # parse the arguments
     args = parser.parse_args(argv)
 
@@ -77,12 +84,12 @@ def main():
 
     if args.format == "mcnp":
         # read the mcnp input
-        input = MCNPInput(filename, args.quick)
+        input = MCNPInput(filename, args.quick, args.preserve_xsid)
         input.read()
         input.process()
     elif args.format == "serpent":
         # read the serpent input
-        input = SerpentInput(filename)
+        input = SerpentInput(filename, args.preserve_xsid)
         input.read()
         input.process()
     elif args.format == "openmc":