NEW YORK, Jan. 30, 2012 /PRNewswire/ -- Post Holdings, Inc. (NYSE: POSTwi) will replace Comstock Resources, Inc. (NYSE: CRK) in the S&P MidCap 400 index, and Comstock Resources will replace THQ Inc. (NASD: THQI) in the S&P SmallCap 600 index after the close of trading on Friday, February 3. S&P MidCap 400 constituent Ralcorp Holdings, Inc. (NYSE: RAH) is spinning off Post Holdings in a transaction expected to be completed on or about that date, pending final approvals. The Ralcorp Holdings stub will remain in the S&P MidCap 400 index. Comstock Resources' market cap is below $620 million, making it more representative of the small cap market space. THQ's market cap is below $50 million, and is no longer representative of the small cap market space.

Post Holdings is a manufacturer, marketer and distributor of ready-to-eat cereal products. Headquartered in St. Louis, MO, the company will be added to the S&P MidCap 400 GICS (Global Industry Classification Standard) Packaged Foods & Meats Sub-Industry index.

Comstock Resources engages in the acquisition, exploration, development, and production of oil and natural gas properties. Headquartered in Frisco, TX, the company will be added to the S&P SmallCap 600 GICS Oil & Gas Exploration & Production Sub-Industry index.

Following is a summary of the changes:

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