CONSTELLATION ENERGY GROUP, INC. INVESTOR RIGHTS AGREEMENT

Exhibit 10.4

CONSTELLATION ENERGY GROUP, INC.

INVESTOR RIGHTS AGREEMENT

SEPTEMBER 19, 2008

TABLE OF CONTENTS

INVESTOR RIGHTS AGREEMENT

     THIS INVESTOR RIGHTS AGREEMENT (this “Agreement”) is made as of the 19 ^th day of September 2008, by and between Constellation Energy Group, Inc., a Maryland corporation (the “Company”) and Mid American Energy Holdings, Inc., an Iowa corporation (the “Investor”).

RECITALS

     WHEREAS, the Investor has, pursuant to that certain Series A Preferred Stock Purchase Agreement dated as of the date hereof (the “Securities Purchase Agreement”) between the Company and the Investor, agreed to purchase shares of the Company’s Series A Convertible Preferred Stock, par value $0.01 per share (the “Series A Preferred Stock”);

     WHEREAS, the shares of Series A Preferred Stock are convertible into shares of the Company’s Common Stock, without par value (the “Common Stock”);

     WHEREAS, in order to induce the Investor to invest funds in the Company, the Company agreed to grant the Investor certain registration rights and other rights as set forth herein;

     NOW, THEREFORE, in consideration of the promises, covenants, and conditions set forth herein, the parties hereto hereby agree as follows:

     1.  Registration Rights . The Company covenants and agrees as follows:

          1.1. Definitions . For purposes of this Agreement:

               (a) The term “Act” means the Securities Act of 1933, as amended.

               (b) The term “Affiliate” means, with respect to any Person, any other Person directly or indirectly controlling, controlled by or under direct or indirect common control with such Person. For the purposes of this definition, “control” when used with respect to any specified Person shall mean the power to direct the management and policies of such Person, directly or indirectly, whether through ownership of voting securities, by contract or otherwise; and the terms “controlled by” and “controlled” have meanings correlative to the foregoing.

               (c) The term “Form S-3” means such form under the Act as in effect on the date hereof or any registration form under the Act subsequently adopted by the SEC that permits inclusion or incorporation of substantial information by reference to other documents filed by the Company with the SEC.

               (d) The term “Holder” means any person owning Registrable Securities or any assignee thereof in accordance with Section 1.13 hereof.

               (e) The term “1934 Act” shall mean the Securities Exchange Act of 1934, as amended.

               (f) The term “register,” “registered,” and “registration” refer to a registration effected by preparing and filing a registration statement or similar document in compliance with the Act, and the declaration or ordering of effectiveness of such registration statement or document.

               (g) The term “Registrable Securities” means (i) the Series A Preferred Stock, (ii) the Common Stock issuable or issued upon conversion of the Series A Preferred Stock, (iii) the 14% Senior Notes (as defined in the Securities Purchase Agreement) issued or issuable upon conversion of the Series A Preferred Stock, (iv) any other shares of Common Stock acquired by the Investor and (v) any Common Stock issued as (or issuable upon the conversion or exercise of any warrant, right or other security that is issued as) a dividend or other distribution with respect to, or in exchange for, or in replacement of, the shares referenced in (i), (ii) and (iv) above; provided, however, that the term “Registrable Securities” shall exclude in all cases any Registrable Securities sold by a person in a transaction in which such person’s rights under this Section 1 are not assigned.

               (h) The number of shares of “Registrable Securities then outstanding” when referring to (i) the Common Stock, shall be determined by the number of shares of Common Stock outstanding that are, and the number of shares of Common Stock issuable pursuant to then exercisable or convertible securities that are, Registrable Securities or (ii) the 14% Senior Notes, shall be determined by the total aggregate principal amount of 14% Senior Notes outstanding at such time.

               (i) The term “SEC” shall mean the Securities and Exchange Commission.

          1.2. Request for Registration .

               (a) Subject to the conditions of this Section 1.2 if the Company shall receive at any time a written request from the Investor, requesting that the Company file a registration statement under the Act covering the registration of a portion of the Registrable Securities then outstanding having an aggregate price to the public (net of any underwriter’s discounts or commissions) of not less than $25,000,000, then the Company shall:

                    (i) within ten (10) days of the receipt thereof, give written notice of such request to all Holders; and

                    (ii) effect as soon as practicable, and in any event within sixty (60) days of the receipt of such request, the registration under the Act of all Registrable Securities that the Holders request to be registered, together with all or such portion of the Registrable Securities of any Holder or Holders joining in such request pursuant to the terms of this Agreement subject to the limitations of subsection 1.2(b), within fifteen (15) days of the mailing of such notice by the Company in accordance with Section 4.5.

               (b) If the Investor intends to distribute the Registrable Securities covered by its request by means of an underwriting, it shall so advise the Company as a part of its request made pursuant to subsection 1.2(a) and the Company shall include such information in the written notice referred to in subsection 1.2(a)(i). The underwriter will be selected by the Investor and shall be reasonably acceptable to the Company. In such event, the right of any Holder to include Registrable Securities in such registration shall be conditioned upon such Holder’s participation in such underwriting to the extent provided herein. All Holders proposing to distribute their securities through such underwriting shall (together with the Company as provided in subsection 1.4(e)) enter into an underwriting agreement in customary form with the underwriter or underwriters selected for such underwriting. Notwithstanding any other provision of this Section 1.2, if the underwriter advises the Investor in writing that marketing factors require a limitation of the number of shares to be underwritten, then the Investor shall so advise all Holders of Registrable Securities that would otherwise be underwritten pursuant hereto, and the number of shares of Registrable Securities that may be included in the underwriting shall be allocated among all Holders electing to include shares in the offering in proportion (as nearly as practicable) to the amount of Registrable Securities of the Company owned by each Holder; provided, however, that the number of shares of Registrable Securities to be included in such underwriting by the Investor shall not be reduced unless all other securities are first entirely excluded from the underwriting.

               (c) Notwithstanding the foregoing, if the Company shall furnish to Holders requesting a registration statement pursuant to this Section 1.2, a certificate signed by the President of the Company stating that in the good faith judgment of a majority of the Board of Directors of the Company it would require the disclosure of material nonpublic information concerning the Company, its business or prospects and that such premature disclosure would be materially adverse to the Company, and/or materially interfere with a pending transaction involving the Company or a subsidiary or controlled Affiliate of the Company, the Company shall have the right to defer taking action with respect to such filing for a period of not more than ninety (90) days after receipt of the request of the Investor; provided, however, that the Company may not utilize this right more than once in any twelve (12) month period.

               (d) In addition, the Company shall not be obligated to effect, or to take any action to effect, any registration pursuant to this Section 1.2:

                    (i) after the Company has effected two (2) registrations pursuant to this Section 1.2 and such registrations have been declared or ordered effective;

                    (ii) during the period starting with the date sixty (60) days prior to the Company’s good faith estimate of the date of filing of, and ending on a date one hundred eighty (180) days after the effective date of, a registration statement filed by the Company subject to Section 1.3 hereof; provided that the Company is actively employing in good faith all reasonable efforts to cause such registration statement to be effective; or

                    (iii) if the Investor proposes to dispose of shares of Registrable Securities that may be immediately registered on Form S-3 pursuant to a request made pursuant to Section 1.12 below.

          1.3. Company Registration . If the Company proposes to register (including for this purpose a registration effected by the Company for stockholders other than the Holders) any of its stock or other securities under the Act in connection with the public offering of such securities solely for cash (other than a registration relating solely to the sale of securities to participants in an employee stock plan or with respect to corporate reorganizations or other transactions under Rule 145 of the Securities Act, or a registration on any form that does not include substantially the same information as would be required to be included in a registration statement covering the sale of the Registrable Securities), the Company shall, at such time, promptly give each Holder written notice of such registration at least ten (10) days prior to the initial filing with the SEC of such registration statement. Upon the written request of each Holder given within twenty (20) days after mailing of such notice, the Company shall, subject to the provisions of Section 1.8, include in the registration statement all of the Registrable Securities that each such Holder has requested to be registered; provided, that the Company may limit, to the extent so advised by the underwriters, the amount of securities to be included in the registration by the Company’s stockholders (including the Holders); provided, however, that the aggregate value of securities (including Registrable Securities) to be included in such registration by the Company’s stockholders (including the Holders) may not be so reduced to less than twenty-five percent (25%) of the total value of all securities included in such registration.

          1.4. Obligations of the Company . Whenever required under this Section 1 to effect the registration of any Registrable Securities, the Company shall, as expeditiously as reasonably possible:

               (a) Prepare and file with the SEC a registration statement with respect to such Registrable Securities and use its reasonable best efforts to cause such registration statement to become effective, and, upon the request of the Holders of a majority of the Registrable Securities registered thereunder, keep such registration statement effective for a period of up to one hundred eighty (180) days;

               (b) Prepare and file with the SEC such amendments and supplements to such registration statement and the prospectus used in connection with such registration statement as may be necessary to comply with the provisions of the Act with respect to the disposition of all securities covered by such registration statement until the earlier of;

                    (i) the time all of such securities have been disposed of; or

                    (ii) the expiration of one hundred eighty (180) days.

               (c) Furnish to the Holders such numbers of copies of a prospectus, including a preliminary prospectus, in conformity with the requirements of the Act, and such other documents as they may reasonably request in order to facilitate the disposition of Registrable Securities owned by them;

               (d) Use its reasonable best efforts to register and qualify the securities covered by such registration statement under such other securities or blue sky laws of such jurisdictions as shall be reasonably requested by the Holders; provided that the Company

shall not be required in connection therewith or as a condition thereto to qualify to do business or to file a general consent to service of process in any such states or jurisdictions;

               (e) In the event of any underwritten public offering, enter into and perform its obligations under an underwriting agreement, in usual and customary form, with the managing underwriter of such offering (each Holder participating in such underwriting shall also enter into and perform its obligations under such an agreement);

               (f) Notify each Holder of Registrable Securities covered by such registration statement at any time when a prospectus relating thereto is required to be delivered under the Act of the happening of any event as a result of which the prospectus included in such registration statement, as then in effect, includes an untrue statement of a material fact or omits to state a material fact required to be stated therein or necessary to make the statements therein not misleading in the light of the circumstances then existing; and at the request of any such Holder promptly prepare and furnish to such Holder a reasonable number of copies of a supplement to or an amendment of such prospectus as may be necessary so that, as thereafter delivered to the purchaser of such shares such prospectus shall not include an untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein not misleading or incomplete in light of the circumstances then existing;

               (g) Cause all such Registrable Securities registered pursuant hereunder to be listed on each securities exchange or nationally recognized quotation system on which similar securities issued by the Company are then listed;

               (h) Use its reasonable best efforts to furnish, at the request of any Holder requesting registration of Registrable Securities pursuant to this Section 1, on the date that such Registrable Securities are delivered to the underwriters for sale in connection with a registration pursuant to this Section 1, if such securities are being sold through underwriters, (i) an opinion, dated such date, of the counsel representing the Company for the purposes of such registration, in substantially the form as may be given to the underwriters in such public offering, addressed to the underwriters, if any, and to the Holders requesting registration of Registrable Securities solely for the purpose of establishing a “due diligence” defense and (ii) a letter dated such date, from the independent certified public accountants of the Company, in substantially the form as may be given by independent certified public accountants to underwriters in such public offering, addressed to the underwriters, if any, and to the Holders requesting registration of Registrable Securities; provided in any such case, the Company is required to provide such opinion or letter, as the case may be, to the underwriters in such offering;

               (i) Make available for inspection by any seller of Registrable Securities, any underwriter participating in any disposition pursuant to such registration statement, and any attorney or accountant retained by any such seller or underwriter, all financial and other records, pertinent corporate documents and properties of the Company, and cause the Company’s officers and directors to supply all information reasonably requested by any such seller, underwriter, attorney or accountant in connection with such registration statement; provided, however, that such seller, underwriter, attorney or accountant shall agree to hold in confidence and trust all information so provided;

               (j) Furnish to each selling Holder a copy of all documents filed with and all correspondence from or to the SEC in connection with any such offering other than non-substantive cover letters and the like; and

               (k) Otherwise use its reasonable best efforts to comply with all applicable rules and regulations of the SEC, and make available to its security holders, as soon as reasonably practicable, an earnings statement covering the period of at least twelve (12) months, but not more than eighteen (18) months, beginning with the first month after the effective date of the registration statement, which earnings statement shall satisfy the provisions of Section 11(a) of the Act.

          1.5. Furnish Information .

     It shall be a condition precedent to the obligations of the Company to take any action pursuant to this Section 1 with respect to the Registrable Securities of any selling Holder that such Holder shall furnish to the Company such information regarding itself, the Registrable Securities held by it, and the intended method of disposition of such securities as shall be required to effect the registration of such Holder’s Registrable Securities.

          1.6. Expenses of Demand Registration . All expenses (other than underwriting discounts and commissions) incurred in connection with registrations, filings or qualifications pursuant to Section 1.2, including (without limitation) all registration, filing and qualification fees, printers’ and accounting fees, blue sky fees and expenses and fees and the reasonable disbursements of counsel for the Company and one counsel for the Holders shall be borne by the Company; provided, however, that the Company shall not be required to pay for any expenses of any registration proceeding begun pursuant to Section 1.2 if the registration request is subsequently withdrawn at the request of the Holders of a majority of the Registrable Securities to be registered (in which case all participating Holders shall bear such expenses), unless the Holders of a majority of the Registrable Securities agree to forfeit their right to one demand registration pursuant to Section 1.2; provided further, however, that if at the time of such withdrawal, the Holders have learned of an adverse change in the condition, business, or prospects of the Company from that known to the Holders at the time of their request and have withdrawn the request with reasonable promptness following disclosure by the Company of such adverse change, then the Holders shall not be required to pay any of such expenses and shall not forfeit their right to one demand registration pursuant to Section 1.2.

          1.7. Expenses of Company Registration . The Company shall bear and pay all expenses incurred in connection with any registration, filing or qualification of Registrable Securities with respect to the registrations pursuant to Section 1.3 for each Holder (which right may be assigned as provided in Section 1.12), including (without limitation) all registration, filing, and qualification fees, printers and accounting fees relating or apportionable thereto, blue sky fees and expenses and the reasonable fees and disbursements of counsel for the Company and one counsel for the selling Holders selected by them, but excluding underwriting discounts and commissions relating to Registrable Securities.

          1.8. Underwriting Requirements . In connection with any offering involving an underwriting of shares of the Company’s capital stock, the Company shall not be

required under Section 1.3 to include any of the Holders’ securities in such underwriting unless they accept the terms of the underwriting reasonably necessary to effect the offer or sale of the Registrable Securities and as agreed upon between the Company and the underwr