| SC 13G/A | 2010-02-16 | FMR LLC | OM GROUP INC | 4,608,001 | 15.1% | EDGAR |
| SC 13G/A | 2010-02-12 | WS MANAGEMENT LLLP | OM GROUP INC | 1,177,222 | 3.8% | EDGAR |
| SC 13G | 2010-02-08 | DIMENSIONAL FUND ADVISORS LP | OM GROUP INC | 2,056,699 | 6.7% | EDGAR |
| SC 13G | 2010-01-29 | BlackRock Inc. | OM GROUP INC | 2,534,011 | 8.3% | EDGAR |
| SC 13G/A | 2009-04-21 | Blenheim Capital Management, L.L.C. | OM GROUP INC | 1,050,000 | 3.5% | EDGAR |
| SC 13G | 2009-02-18 | STATE STREET BANK & TRUST CO | OM GROUP INC | 603,346 | 2.0% | EDGAR |
| SC 13G/A | 2009-02-17 | FMR LLC | OM GROUP INC | 4,575,601 | 15.0% | EDGAR |
| SC 13G/A | 2009-02-13 | WS MANAGEMENT LLP | OM GROUP INC | 2,093,800 | 6.9% | EDGAR |
| SC 13G/A | 2009-02-13 | CITADEL ADVISORS LLC | OM GROUP INC | 37,700 | - | EDGAR |
| SC 13G/A | 2009-02-12 | GENDELL JEFFREY L ET AL | OM GROUP INC | 86,917 | 0.3% | EDGAR |
| SC 13G | 2009-02-05 | BARCLAYS GLOBAL INVESTORS NA /CA/ | OM GROUP INC | 690,836 | 2.3% | EDGAR |
| SC 13G/A | 2009-01-07 | SAC CAPITAL ADVISORS LLC | OM GROUP INC | 0 | 0.0% | EDGAR |
| SC 13G | 2008-10-31 | WS MANAGEMENT LLP | OM GROUP INC | 1,708,800 | 5.6% | EDGAR |
| SC 13G | 2008-08-15 | GENDELL JEFFREY L ET AL | OM GROUP INC | 302,400 | 1.0% | EDGAR |
| SC 13G | 2008-07-31 | CITADEL INVESTMENT GROUP LLC | OM GROUP INC | 1,615,916 | - | EDGAR |
| SC 13G | 2008-05-15 | Blenheim Capital Management, L.L.C. | OM GROUP INC | 1,558,500 | 5.1% | EDGAR |
| SC 13G | 2008-05-05 | STATE STREET BANK & TRUST CO | OM GROUP INC | 1,656,645 | 5.4% | EDGAR |
| SC 13G/A | 2008-02-14 | SAC CAPITAL ADVISORS LLC | OM GROUP INC | 1,027,000 | 3.4% | EDGAR |
| SC 13G | 2008-02-06 | BARCLAYS GLOBAL INVESTORS NA /CA/ | OM GROUP INC | 751,546 | 2.5% | EDGAR |
| SC 13G/A | 2008-01-10 | FMR LLC | OM GROUP INC | 4,562,865 | 15.0% | EDGAR |