Annaly Capital (NLY), a real estate investment trust, will offer 100 million shares of common stock and use the funds for buying mortgage-backed securities. The firm did not immediately release how much they expect to raise from the stock offer, but on Monday, Annaly stock traded at more than $18 per share. Underwriters of the offering will be given a 30-day option to buy another 15 million shares in common stock to cover overallotments. Credit Suisse (CS) will be the lead book-running manager on the deal. Annaly raised $1.1 billion in capital from a stock offering in July 2010 and another $1.3 billion in January. According to JPMorgan Chase (JPM) analysts, REITs could buy as much  as $100 billion in MBS by the end of the year. Write to Jon Prior. Follow him on Twitter @JonAPrior.