U.S. stocks kicked off a shortened trading week slightly to the downside as oil prices lost steam on supply concerns. U.S. stocks have been rallying for the past five weeks, but analysts are wary that the gains will continue. 'It seems to me that markets are currently trading on fumes,' said Michael Ingram, a market analyst with BGC Partners, in London. 'Perhaps understandable after the central bank heavy week that we've just exited.' Meanwhile, Starwood Hotels (HOT) agreed to a strengthened takeover bid from Marriott International (MAR - Get Report) - pegging the value of the hotel chain at $13.6 billion. Last week, Starwood reached a deal with China-based Anbang that would have valued Starwood at a just $13.2 billion. Starwood is a holding of Jim Cramer's charitable trust, Action Alerts PLUS. Finally, Priceline Group (PCLN) has reached a deal with Cuba to allow Americans to book hotels on the island through one of its travel websites, Booking.com. On Sunday, President Obama traveled to Havana in a historic visit that marks the normalization of relations between the two nations. TheStreet's Scott Gamm reports from Wall Street.