SC 13G 1 ari13g-plx.txt PLAINS RESOURCES INC. UNITED STATES SECURITIES AND EXCHANGE COMMISSION "Washington, DC 20549" SCHEDULE 13G Under the Securities and Exchange Act of 1934 (Amendment No. ______________)* Plains Resources Inc. ------------------------------------------------------------------ (Name of Issuer) Common ------------------------------------------------------------------ (Title of Class of Securities) 726540503 ------------------------------------------------------------------ (CUSIP Number) December 31, 2002 ------------------------------------------------------------------ (Date of Event Which Requires Filing of this Statement) Check the apprpriate box to designate the rule pursuant to which this Schedule is filed: [X] Rule 13d-1 (b) [ ] Rule 13d-1 (c) [ ] Rule 13d-1 (d) * The remainder of this cover page shall be filled out for a reporting person's initial filing on this form with respect to the subject class of securites, and for any subsequent amendment containing information which would alter the disclosures provided in a prior cover page. The information required in the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act, but shall be subject to all other provisions of the Act (however, see the Notes.) 1 Name of Reporting Person / IRS Identification Number: Advisory Research, Inc. / 36-2831881 ------------------------------------------------------------------ 2 Check the Appropriate Box if a Member of a Group (a) [ ] (See Instructions) (b) [X] ------------------------------------------------------------------ 3 SEC Use Only ------------------------------------------------------------------ 4 Citizenship or Place of Organization Delaware ------------------------------------------------------------------ Number of 5 Sole Voting Power Shares 1,181,894 Shares ----------------------------------------------- Beneficially 6 Shared Voting Power Owned By 0 Shares ----------------------------------------------- Each 7 Sole Dispositive Power Reporting 1,181,894 Shares ----------------------------------------------- Person 8 Shared Dispositive Power With 0 Shares ------------------------------------------------------------------ 9 Aggregate Amount Beneficially Owned by Each Reporting Person 1,181,894 Shares ------------------------------------------------------------------ 10 Check if the Aggregate Amount in Row (9) Excludes Certain Shares [ ] (See Instructions) ------------------------------------------------------------------ 11 Percent of Class Represented by Amount in Row (9) 4.91% ------------------------------------------------------------------ 12 Type of Reporting Person IA ------------------------------------------------------------------ Item 1 (a) Name of Issuer: Plains Resources Inc. Item 1 (b) Name of Issuer's Principal Executive Offices: 500 Dallas Street Suite 700 Houston, TX 77002 Item 2 (a) Person Filing - Advisory Research, Inc. Item 2 (b) Address - 180 North Stetson St., Suite 5780 Chicago, IL 60601 Item 2 (c) Citizenship - Advisory Research, Inc. is a Delaware Corporation Item 2 (d) Title of Class of Securities - Common Item 2 (e) CUSIP Number - 726540503 Item 3 If this statement is filed pursuant to Rules 13d-1(b) or 13d-2(b), check whether the person filing is a: (a) [ ] Broker or Dealer registered under Section 15 of the Act (b) [ ] Bank as defined in Section 3(a)(6) of the Act (c) [ ] Insurance Company as defined in Section 3(a)(19) of the Act (d) [ ] Investment Company registered under Section 8 of the Investment Company Act (e) [X] Investment Advisor in accordance with section 240.13d-1(b)(1)(ii)(E) (f) [ ] Employee Benefit Plan or Endowment Fund in accordance with section 240.13d-1(b) (1)(ii)(F) (g) [ ] Parent Holding Company or Control Person in accordance with secton 13d-1(b) (1)(ii)(G) (h) [ ] A savings association as defined in section 3(b) of the Federal Deposit Insurance Act (i) [ ] A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 Item 4 Ownership (a) Amount Beneficially Owned: Advisory Research, Inc. 1,181,894 Shares (b) Percent of Class 4.91% (c) Number of shares as to which reporting person has: (i) Sole Voting Power 1,181,894 Shares (ii) Shared Voting Power 0 Shares (iii) Sole Dispositive Power 1,181,894 Shares (iv) Shared Dispositive Power 0 Shares Item 5 Ownership of Five Percent or Less of a Class: If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following [X] Item 6 Ownership of More than Five Percent on Behalf of Another Person: Not Applicable Item 7 Identification and Classification of the Subsidiary Which Acquired the Security being Reported on by the Parent Holding Company: Not Applicable Item 8 Identification and Classification if Members of the Group: Not Applicable Item 9 Notice of Dissolution of Group: Not Applicable Item 10 Certification By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of such securities and were not acquired and are not held in connection with or as a participant in any transaction having such purposes or effect. SIGNATURE After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct. February 12, 2003 ---------------------------------- Date /s/ Brien M. O'Brien ---------------------------------- Signature Brien M. O'Brien, Chairman ---------------------------------- Name/Title