Oil erases gains as demand worries outweigh OPEC Futures pull back after topping $50 a barrel for the first time in two weeks <a href="http://www.marketwatch.com/news/story/oil-tops-50-first-time/story.aspx?guid" target="_blank">http://www.marketwatch.com/news/story/oil-tops-50-first-time/story.aspx?guid</a>={1C00DB8C-CC02-45ED-8CC4-EE53F6141A9B}&siteid=yahoomy