Exhibit 24

                                POWER OF ATTORNEY

     KNOW ALL MEN BY THESE PRESENTS: That the undersigned has made, constituted
and appointed, and by this instrument does make, constitute and appoint ROBERT
PIERCE, ELIZABETH SHAUGHNESSY and CIPRIANO BEREDO, acting individually, as his
or her true and lawful attorney, for him or her, and in his or her name, place
and stead, to affix, as attorney-in-fact, the signature of the undersigned to
any reports or filings to the Securities and Exchange Commission on or in
connection with Forms 3, 4, 5 or 144 with respect to transactions or holdings by
the undersigned in equity securities issued by OM Group, Inc., a Delaware
corporation, and to any and all amendments to such reports, giving and granting
unto each such attorney-in-fact full power and authority to do and perform every
act and thing whatsoever necessary to be done in the premises, as fully as the
undersigned might or could do if personally present, hereby ratifying and
confirming all that each such attorney-in-fact shall lawfully do or cause to be
done by virtue hereof.

     This Power of Attorney shall expire on the date the undersigned is no
longer required to file Forms 3, 4, 5 or 144 reports with the Securities and
Exchange Commission with respect to holdings of and transactions in securities
issued by OM Group, Inc., unless revoked in writing prior thereto.

     IN WITNESS WHEREOF, this Power of Attorney has been signed at Key Tower,
Cleveland, Ohio, as of the 2nd day of May, 2006.


                                        /s/ Marcus P. Bak
                                        ----------------------------------------
                                            Marcus P. Bak