The stock purchases were made by entities that are owned and controlled by Zell or are trustees in various trusts established for the benefit of Zell and his family, the filing further states. Zell now has a 7.7% stake in Starwood based on approximately 191 million shares outstanding as of Dec. 31.

In the filing, Zell states that the general partner of the utilized working capital and from brokerage account margin loans "maintained in the ordinary course of doing business" to purchase the stock. The stock purchases were made "solely for the purpose of investment." It adds that the general partner "has no intention of participating in the formulation, determination or direction of the basic business decisions" of Starwood or any of its affiliates.

In early morning trading on Tuesday, Starwood's stock was selling at $47.52 a share, up $1.33 a share from Monday's closing price of $46.19 a share.

Starwood, which expects to open its 900th hotel this year, reports that it plans to increase its portfolio by 50% in the next five years. Its active pipeline includes 500 hotels and 120,000 rooms. This year, Starwood expects to add 80 to 100 hotels to its portfolio, a 50% increase from hotel openings posted in 2007.