diff -r d0b0ff0594db Include/sysmodule.h
--- a/Include/sysmodule.h	Wed Oct 13 19:14:16 2010 +0200
+++ b/Include/sysmodule.h	Wed Oct 13 20:58:52 2010 +0200
@@ -27,6 +27,9 @@ PyAPI_FUNC(void) PySys_AddWarnOption(con
 PyAPI_FUNC(void) PySys_AddWarnOptionUnicode(PyObject *);
 PyAPI_FUNC(int) PySys_HasWarnOptions(void);
 
+PyAPI_FUNC(void) PySys_AddXOption(const wchar_t *);
+PyAPI_FUNC(PyObject *) PySys_GetXOptions(void);
+
 #ifdef __cplusplus
 }
 #endif
diff -r d0b0ff0594db Lib/test/test_cmd_line.py
--- a/Lib/test/test_cmd_line.py	Wed Oct 13 19:14:16 2010 +0200
+++ b/Lib/test/test_cmd_line.py	Wed Oct 13 20:58:52 2010 +0200
@@ -67,6 +67,16 @@ class CmdLineTest(unittest.TestCase):
         rc, out, err = assert_python_ok('-vv')
         self.assertNotIn(b'stack overflow', err)
 
+    def test_xoptions(self):
+        rc, out, err = assert_python_ok('-c', 'import sys; print(sys.xoptions)')
+        opts = eval(out.splitlines()[0])
+        self.assertEqual(opts, {})
+        rc, out, err = assert_python_ok(
+            '-Xa,b=c,d', '-Xe,f=g=h', '-c', 'import sys; print(sys.xoptions)')
+        opts = eval(out.splitlines()[0])
+        self.assertEqual(opts,
+            {'a': True, 'b': 'c', 'd': True, 'e': True, 'f': 'g=h' })
+
     def test_run_module(self):
         # Test expected operation of the '-m' switch
         # Switch needs an argument
diff -r d0b0ff0594db Modules/main.c
--- a/Modules/main.c	Wed Oct 13 19:14:16 2010 +0200
+++ b/Modules/main.c	Wed Oct 13 20:58:52 2010 +0200
@@ -47,7 +47,7 @@ static wchar_t **orig_argv;
 static int  orig_argc;
 
 /* command line options */
-#define BASE_OPTS L"bBc:dEhiJm:OsStuvVW:xX?"
+#define BASE_OPTS L"bBc:dEhiJm:OsStuvVW:xX:?"
 
 #define PROGRAM_OPTS BASE_OPTS
 
@@ -84,6 +84,7 @@ static char *usage_3 = "\
 -W arg : warning control; arg is action:message:category:module:lineno\n\
          also PYTHONWARNINGS=arg\n\
 -x     : skip first line of source, allowing use of non-Unix forms of #!cmd\n\
+-X opt : set implementation-specific option\n\
 ";
 static char *usage_4 = "\
 file   : program read from script file\n\
@@ -410,8 +411,6 @@ Py_Main(int argc, wchar_t **argv)
             skipfirstline = 1;
             break;
 
-        /* case 'X': reserved for implementation-specific arguments */
-
         case 'h':
         case '?':
             help++;
@@ -425,6 +424,10 @@ Py_Main(int argc, wchar_t **argv)
             PySys_AddWarnOption(_PyOS_optarg);
             break;
 
+        case 'X':
+            PySys_AddXOption(_PyOS_optarg);
+            break;
+
         /* This space reserved for other options */
 
         default:
diff -r d0b0ff0594db Python/getopt.c
--- a/Python/getopt.c	Wed Oct 13 19:14:16 2010 +0200
+++ b/Python/getopt.c	Wed Oct 13 20:58:52 2010 +0200
@@ -89,12 +89,6 @@ int _PyOS_GetOpt(int argc, wchar_t **arg
         return '_';
     }
 
-    if (option == 'X') {
-        fprintf(stderr,
-          "-X is reserved for implementation-specific arguments\n");
-        return '_';
-    }
-
     if ((ptr = wcschr(optstring, option)) == NULL) {
         if (_PyOS_opterr)
           fprintf(stderr, "Unknown option: -%c\n", (char)option);
diff -r d0b0ff0594db Python/sysmodule.c
--- a/Python/sysmodule.c	Wed Oct 13 19:14:16 2010 +0200
+++ b/Python/sysmodule.c	Wed Oct 13 20:58:52 2010 +0200
@@ -1086,6 +1086,76 @@ PySys_HasWarnOptions(void)
     return (warnoptions != NULL && (PyList_Size(warnoptions) > 0)) ? 1 : 0;
 }
 
+static PyObject *xoptions = NULL;
+
+static PyObject *
+get_xoptions(void)
+{
+    if (xoptions == NULL || !PyDict_Check(xoptions)) {
+        Py_XDECREF(xoptions);
+        xoptions = PyDict_New();
+    }
+    return xoptions;
+}
+
+void
+PySys_AddXOption(const wchar_t *s)
+{
+    PyObject *opts;
+    PyObject *name = NULL, *value = NULL;
+    const wchar_t *name_end, *opt_end;
+    int r;
+
+    opts = get_xoptions();
+    if (opts == NULL)
+        goto error;
+
+    for (;;) {
+        opt_end = wcschr(s, L',');
+        name_end = wcschr(s, L'=');
+        if (!name_end || (opt_end && name_end > opt_end)) {
+            name_end = opt_end;
+            value = Py_True;
+            Py_INCREF(value);
+        }
+        else {
+            if (opt_end)
+                value = PyUnicode_FromWideChar(name_end + 1, opt_end - (name_end + 1));
+            else
+                value = PyUnicode_FromWideChar(name_end + 1, -1);
+            if (value == NULL)
+                goto error;
+        }
+        if (name_end)
+            name = PyUnicode_FromWideChar(s, name_end - s);
+        else
+            name = PyUnicode_FromWideChar(s, -1);
+        if (name == NULL)
+            goto error;
+        r = PyDict_SetItem(opts, name, value);
+        Py_DECREF(name);
+        Py_DECREF(value);
+        if (!opt_end)
+            break;
+        s = opt_end + 1;
+    }
+
+    return;
+
+error:
+    Py_XDECREF(name);
+    Py_XDECREF(value);
+    /* No return value, therefore clear error state if possible */
+    if (_Py_atomic_load_relaxed(&_PyThreadState_Current))
+        PyErr_Clear();
+}
+
+PyObject *
+PySys_GetXOptions(void)
+{
+    return get_xoptions();
+}
+
 /* XXX This doc string is too long to be a single string literal in VC++ 5.0.
    Two literals concatenated works just fine.  If you have a K&R compiler
    or other abomination that however *does* understand longer strings,
@@ -1531,6 +1601,11 @@ _PySys_Init(void)
         PyDict_SetItemString(sysdict, "warnoptions", warnoptions);
     }
 
+    v = get_xoptions();
+    if (v != NULL) {
+        PyDict_SetItemString(sysdict, "xoptions", v);
+    }
+
     /* version_info */
     if (VersionInfoType.tp_name == 0)
         PyStructSequence_InitType(&VersionInfoType, &version_info_desc);