Index: Lib/argparse.py
===================================================================
--- Lib/argparse.py	(revision 86616)
+++ Lib/argparse.py	(working copy)
@@ -382,6 +382,9 @@
         # find group indices and identify actions in groups
         group_actions = set()
         inserts = {}
+        variable_option_usage = any(
+            a.nargs in (OPTIONAL, ONE_OR_MORE, ZERO_OR_MORE)
+            for a in actions if a.option_strings)
         for group in groups:
             try:
                 start = actions.index(group._group_actions[0])
@@ -422,6 +425,11 @@
 
             # produce all arg strings
             elif not action.option_strings:
+                # add -- before the first argument if needed to be unambiguous
+                if variable_option_usage:
+                    parts.append("--")
+                    variable_option_usage = False
+
                 part = self._format_args(action, action.dest)
 
                 # if it's in a group, strip the outer []
Index: Lib/test/test_argparse.py
===================================================================
--- Lib/test/test_argparse.py	(revision 86616)
+++ Lib/test/test_argparse.py	(working copy)
@@ -1238,9 +1238,38 @@
         ('a', NS(x=None, y=['a'])),
         ('a -x', NS(x=[], y=['a'])),
         ('a -x b', NS(x=['b'], y=['a'])),
+        ('-x a b', NS(x=['a','b'], y=[])),
+        ('-x -- a b', NS(x=[], y=['a', 'b']))
     ]
 
 
+class TestNargsZeroOrOne(ParserTestCase):
+    """Tests specifying an args for an Optional that accepts zero or more"""
+
+    argument_signatures = [Sig('-x', nargs='?'), Sig('y', nargs='?')]
+    failures = ["-x a b c", "a b -x"]
+    successes = [
+        ('', NS(x=None, y=None)),
+        ('-x', NS(x=None, y=None)),
+        ('-x a', NS(x='a', y=None)),
+        ('-x -- a', NS(x=None, y='a')),
+        ('a', NS(x=None, y='a')),
+        ('a -x', NS(x=None, y='a')),
+        ('a -x b', NS(x='b', y='a')),
+        ('-x a -- b', NS(x='a', y='b'))
+    ]
+
+
+class TestNargsOneOrMore(ParserTestCase):
+    """Tests specifying an args for an Optional that accepts one or more"""
+
+    argument_signatures = [Sig('-x', nargs='+'), Sig('y')]
+    failures = ['-x a b']
+    successes = [
+        ('-x a -- b', NS(x=['a'], y='b')),
+        ('b -x a', NS(x=['a'], y='b'))
+    ]
+
 class TestNargsRemainder(ParserTestCase):
     """Tests specifying a positional with nargs=REMAINDER"""
 
@@ -2856,7 +2885,7 @@
             Sig('-z', nargs='+', help='Z HELP')]),
     ]
     usage = '''\
-        usage: PROG [-h] [-v] [-x] [--y Y] [-z Z [Z ...]] foo bar baz
+        usage: PROG [-h] [-v] [-x] [--y Y] [-z Z [Z ...]] -- foo bar baz
         '''
     help = usage + '''\
 
@@ -3847,6 +3876,107 @@
         '''
     version = ''
 
+class TestHelpZeroOrOneOptionalsNoPositionals(HelpTestCase):
+    """Test lacking of -- seperator if no positional arguments can be supplied
+    """
+
+    parser_signature = Sig(prog='PROG')
+    argument_signatures = [Sig('-x', nargs='?')]
+    argument_group_signatures = []
+    usage = '''\
+        usage: PROG [-h] [-x [X]]
+        '''
+    help = usage + '''\
+
+        optional arguments:
+          -h, --help  show this help message and exit
+          -x [X]
+        '''
+    version= ''
+
+class TestHelpOneOrMoreOptionalsNoPositionals(HelpTestCase):
+    """Test lacking of -- seperator if no positional arguments can be supplied
+    """
+
+    parser_signature = Sig(prog='PROG')
+    argument_signatures = [Sig('-x', nargs='+')]
+    argument_group_signatures = []
+    usage = '''\
+        usage: PROG [-h] [-x X [X ...]]
+        '''
+    help = usage + '''\
+
+        optional arguments:
+          -h, --help    show this help message and exit
+          -x X [X ...]
+        '''
+    version= ''
+
+class TestHelpOneOrMoreOptionalsNoPositionals2(HelpTestCase):
+    """Test lacking of -- seperator if no positional arguments can be supplied
+    """
+
+    parser_signature = Sig(prog='PROG')
+    argument_signatures = [Sig('-x', nargs='+'), Sig('-y')]
+    argument_group_signatures = []
+    usage = '''\
+        usage: PROG [-h] [-x X [X ...]] [-y Y]
+        '''
+    help = usage + '''\
+
+        optional arguments:
+          -h, --help    show this help message and exit
+          -x X [X ...]
+          -y Y
+        '''
+    version= ''
+
+class TestHelpMiscOptionalsWithPositionals(HelpTestCase):
+    """Test output of -- seperator if some positional arguments follow
+       optionals with variable length
+    """
+
+    parser_signature = Sig(prog='PROG')
+    argument_signatures = [Sig('-x', nargs='+'), Sig('-y'), Sig("z")]
+    argument_group_signatures = []
+    usage = '''\
+        usage: PROG [-h] [-x X [X ...]] [-y Y] -- z
+        '''
+    help = usage + '''\
+
+        positional arguments:
+          z
+
+        optional arguments:
+          -h, --help    show this help message and exit
+          -x X [X ...]
+          -y Y
+        '''
+    version= ''
+
+class TestHelpZeroOrOneOptionalWithZeroOrOnePositional(HelpTestCase):
+    """Test output of -- seperator if some positional arguments follow
+       optionals with variable length
+    """
+
+    parser_signature = Sig(prog='PROG')
+    argument_signatures = [Sig('-x', nargs='?'), Sig("z", nargs="?")]
+    argument_group_signatures = []
+    usage = '''\
+        usage: PROG [-h] [-x [X]] -- [z]
+        '''
+    help = usage + '''\
+
+        positional arguments:
+          z
+
+        optional arguments:
+          -h, --help  show this help message and exit
+          -x [X]
+        '''
+    version= ''
+
+
 # =====================================
 # Optional/Positional constructor tests
 # =====================================