UPDATE 1-SandRidge Energy's trust unit files for IPO

* Morgan Stanley, Raymond James to underwrite offering

* Trust to offer 25 mln common units

Jan 5 (Reuters) - SandRidge Energy's trust unit, SandRidge Mississippian Trust II, filed with U.S. regulators on Thursday to raise up to $603.75 million in an initial public offering of its common stock.

In a filing with the U.S. Securities and Exchange Commission, SandRidge Energy said Morgan Stanley and Raymond James will underwrite its unit's offering.

The Oklahoma City, Oklahoma-based company said the trust will offer up to 25 million common units, which it intends to list on the New York Stock Exchange under the symbol "SDR."

The filing said the trust will deliver the net proceeds to one or more of SandRidge's units as consideration for royalties.

The amount of money a company says it plans to raise in its first IPO filings is used to calculate registration fees. The final size of the IPO could be different.