Filed by Mirant Corporation

Pursuant to Rule 425 under the Securities Act of 1933

and deemed filed pursuant to Rule 14a-12

of the Securities Exchange Act of 1934, as amended

Subject Company: Mirant Corporation

(Commission File No. 001-16107)

Below is a copy of the presentation that was given by Mirant on its First Quarter 2010 Earnings Results on May 7, 2010

Dickerson  Generating Station Mirant Corporation First Quarter 2010 Earnings Results May 7, 2010

2 Safe Harbor Statement Forward-Looking Statements This presentation may contain statements, estimates or projections that constitute “forward-looking statements” as defined under U.S. federal securities laws. In some cases, one can identify forward-looking statements by terminology such as “will,” “expect,” “plan,” “lead,” “project” or the negative of these terms or other comparable terminology. Forward-looking statements are subject to certain risks and uncertainties that could cause actual results to differ materially from Mirant’s historical experience and our present expectations or projections. These risks include, but are not limited to: (i) legislative and regulatory initiatives relating to the electric utility industry; (ii) changes in, or changes in the application of, environmental or other laws; (iii) failure of our assets to perform as expected, including due to outages for unscheduled maintenance or repair; (iv) changes in market conditions or the entry of additional competition in our markets; (v) the expected timing and likelihood of completion of the proposed merger with RRI Energy, including the timing, receipt and terms and conditions of required stockholder, governmental and regulatory approvals that may reduce anticipated benefits or cause the parties to abandon the merger; the ability of the parties to arrange debt financing in an amount sufficient to fund the refinancing contemplated in, and on terms consistent with, the Merger Agreement; the diversion of management’s time and attention from our ongoing business during the time we are seeking to complete the merger; the ability to maintain relationships with employees, customers and suppliers; the ability to integrate successfully the businesses and realize cost savings and any other synergies; and the risk that credit ratings of the combined company or its subsidiaries may be different from what the companies expect; and (vi) those factors contained in our periodic reports filed with the SEC, including in our Annual Report on Form 10-K for the year ended December 31, 2009 and our Quarterly Report on Form 10-Q for the period ended March 31, 2010. The forward-looking information in this document is given as of this date only, and Mirant assumes no duty to update this information. Additional Information and Where To Find It  This communication does not constitute an offer to sell or the solicitation of an offer to buy any securities or a solicitation of any vote or approval nor shall there be any sale of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. In connection with the proposed merger between RRI Energy and Mirant, RRI Energy will file with the SEC a Registration Statement on Form S-4 that will include a joint proxy statement of RRI Energy and Mirant that also constitutes a prospectus of RRI Energy. RRI Energy and Mirant will mail the joint proxy statement/prospectus to their respective shareholders. RRI Energy and Mirant urge investors and shareholders to read the joint proxy statement/prospectus regarding the proposed merger when it becomes available, as well as other documents filed with the SEC, because they will contain important information. You may obtain copies of all documents filed with the SEC regarding this transaction, free of charge, at the SEC’s website (www.sec.gov). You may also obtain these documents, free of charge, from RRI Energy’s website (www.rrienergy.com) under the tab “Investor Relations” and then under the heading “Company Filings.” You may also obtain these documents, free of charge, from Mirant’s website (www.mirant.com) under the tab “Investor Relations” and then under the heading “SEC Filings.”

3 Safe Harbor Statement Participants in The Merger Solicitation  RRI Energy, Mirant, and their respective directors, executive officers and certain other members of management and employees may be soliciting proxies from RRI Energy and Mirant shareholders in favor of the merger and related matters. Information regarding the persons who may, under the rules of the SEC, be deemed participants in the solicitation of RRI Energy and Mirant shareholders in connection with the proposed merger will be set forth in the joint proxy statement/prospectus when it is filed with the SEC. You can find information about RRI Energy’s executive officers and directors in its definitive proxy statement filed with the SEC on April 1, 2010. You can find information about Mirant’s executive officers and directors in its definitive proxy statement filed with the SEC on March 26, 2010 and supplemented on April 28, 2010. Additional information about RRI Energy’s executive officers and directors and Mirant’s executive officers and directors can be found in the above-referenced Registration Statement on Form S-4 when it becomes available. You can obtain free copies of these documents from RRI Energy and Mirant using the contact information above. Non-GAAP Financial Information The following presentation includes certain “non-GAAP financial measures” as defined in Regulation G under the Securities Exchange Act of 1934. A schedule is attached hereto and is posted on the Company’s website at mirant.com (in the Investor Relations - Presentations section) that reconciles the non-GAAP financial measures included in the following presentation to the most directly comparable financial measures calculated and presented in accordance with Generally Accepted Accounting Principles. In addition, the Company has included a more detailed description of each of the non-GAAP financial measures used in this presentation, together with a discussion of the usefulness and purpose of these measures as Exhibit 99.2 to the Company’s Current Report on Form 8-K furnished to the SEC with its earnings press release.

4 Highlights On April 11, 2010, Mirant and RRI Energy announced that the companies would merge to form GenOn Energy Creation of GenOn Energy will deliver significant value to stockholders Strategic rationale for the transaction Significant near-term value creation driven by annual cost savings of $150 million to be fully realized starting in January 2012 Strengthened balance sheet and enhanced financial flexibility Increased scale and geographic diversity across key regions Well positioned to benefit from improvement in market fundamentals Merger is expected to close by the end of 2010 Operational Performance - Cash Generation - Prudent Growth

5 GenOn Energy - Steps to Close Planned refinancing Expect to replace each company’s revolving credit facilities in a new holding company facility Address $1.8 billion of debt MNA Senior Secured Term Loan ($307MM due 2013) MNA Senior Notes ($850MM of 7.375% notes due 2013) RRI Energy Secured Bonds ($279MM due 2014) PEDFA Secured Notes ($371MM due 2036) Mirant and RRI Energy stockholder approval Regulatory approvals Federal Energy Regulatory Commission (FERC) Hart-Scott-Rodino (HSR) Review New York State Public Service Commission Filed April 23, 2010 Operational Performance - Cash Generation - Prudent Growth

6 Financial Highlights ($millions) Change in Adjusted EBITDA principally attributable to - Lower realized value of hedges - Lower energy gross margins from Northeast generation - Lower net gains from sales of emissions allowances Higher energy gross margins from Mid-Atlantic generation Operational Performance - Cash Generation - Prudent Growth Adjusted EBITDA 162 195 Q1 2010 2009

7 Operations Highlights Mirant’s safety incident rates remain at historically low levels Commercial Availability, the percent of maximum achievable energy gross margin that was realized in the period, continues to improve Commercial Availability Safety Incident Rates Lost Time Incident Rate Lost Time EEI Top Quartile Benchmark Recordable Incident Rate Recordable EEI Top Quartile Benchmark

8 Market Update Since February Operational Performance - Cash Generation - Prudent Growth Near term (2010) Natural gas prices decreased and currently trade around $4.50/mmBtu for the balance of the year Power prices in PJM decreased Northern Appalachian coal prices decreased modestly and trade around $52/ton Dark spreads decreased Longer term (2011 – 2014) Natural gas prices decreased and currently trade in a range of $5.40 to $6.40/mmBtu Power prices in PJM decreased Northern Appalachian coal prices were relatively unchanged and are quoted in a range of $62– $75/ton Dark spreads decreased

9 8% 12% 16% 20% 24% 28% 32% 36% 40% 2010 2011 2012 2013 2014 New York East N.California PJM East New England PJM RTO (ex. COMED) Target Reserve range Electricity Markets Reserve Margins Operational Performance - Cash Generation - Prudent Growth Forecasted reserve margins incorporate the latest information from each ISO Supply/demand imbalance is delayed, but the trend remains the same Source:  Mirant forecasts

10 Hedge Levels Based on Expected Total Generation Operational Performance - Cash Generation - Prudent Growth 1. Positions as of April 13, 2010; shaded boxes represent net additions to prior guidance 2. 2010 represents period between May and December 3. Power hedges include hedges with both power and natural gas Aggregate Baseload Coal

11 Marsh Landing Generating Station Operational Performance - Cash Generation - Prudent Growth By Q3 2010, we expect Issuance of permits Draft Air Permit issued by the Bay Area Air Quality Management District on March 29, 2010 California Energy Commission Staff Assessment issued on April 23, 2010 CPUC approval of the PPA Project financing to close

12 Marsh Landing Generating Station (Cont.) Operational Performance - Cash Generation - Prudent Growth All-in funding requirement is expected to be slightly above $700 million Amount includes costs for construction, equipment, supplies, debt service reserve, capitalized interest, transmission upgrades and other capitalized costs Construction expected to begin in late 2010 and to be completed by mid-2013 EPC contract with Kiewit signed on May 6, 2010

13 Financial Results (millions, except per share amounts) Operational Performance - Cash Generation - Prudent Growth 2010 2009 Net income 407 $    380 $    Unrealized gains on derivatives (352)     (254)     Lower of cost or market inventory adjustments, net 3           (12)       Other 3 1           Adjusted net income 61 115 Interest, taxes, depreciation & amortization 101 80         Adjusted EBITDA 162 $    195 $    Diluted weighted average shares outstanding 146       145       Earnings per share: Net income 2.79 $   2.62 $   Adjusted net income 0.42 $   0.79 $   Q1

14 Realized Gross Margin (millions) Operational Performance - Cash Generation - Prudent Growth

15 Adjusted Free Cash Flow (millions, except per share amounts) Operational Performance - Cash Generation - Prudent Growth 2010 2009 Net cash provided by operating activities 302 $    271 $            Bankruptcy claim payments -            1                   Emission allowance sales proceeds 2           15                 Capitalized interest -            (2)            Adjusted net cash provided by operating activities 304       285          Capital expenditures, excluding capitalized interest (85)        (169)        Adjusted free cash flow 219       116               MD Healthy Air Act capital expenditures 48         122          Adjusted free cash flow (w/o MD HAA) 267 $    238 $            Diluted weighted average shares outstanding 146       145          Adjusted free cash flow per share (w/o MD HAA) 1.83 $   1.64 $      Q1

16 Consolidated Debt and Liquidity (millions) Operational Performance - Cash Generation - Prudent Growth Debt $        2,564 Cash and cash equivalents Mirant Corporation 1,505 $        Mirant Americas Generation 20                Mirant North America 356              Mirant Mid-Atlantic 197              Other 27                Total cash and cash equivalents 2,105           Less restricted and reserved (11)               Available cash & cash equivalents 2,094           Revolver & LC availability 635              Total available liquidity 2,729 $        March 31, 2010

17 Capital Expenditures (millions) Maryland Healthy Air Act spending prior to 2010 totaled approximately $1.405 billion Normalized maintenance CapEx of $50 million to $60 million per year Other environmental expenditures include the remaining $33 million deposited in escrow for control of small dust particles as a result of the Potomac River agreement Operational Performance - Cash Generation - Prudent Growth 2010 1 2011 Environmental Maryland Healthy Air Act 269 $      - $        Other 10 29 Maintenance 105 48 Construction Marsh Landing Generating Station 47 185 Other 31 43 Other 18 11 Total Capital Expenditures 2 480 $      316 $      1 Includes actuals for January through March 2 Excludes capitalized interest unrelated to the Marsh Landing project financing Forecast

18 Takeaways Creation of GenOn Energy will deliver significant value to stockholders Hedging cushioned Mirant in Q1 2010 from the effects of relatively low commodity prices The supply/demand balance is forecasted to tighten, although at a slower pace than previously projected Mirant continues to make progress to permit, finance and commence construction of its Marsh Landing generating facility later in 2010 Operational Performance - Cash Generation - Prudent Growth

Dickerson  Generating Station Appendix

20 Federal NOL Update Operational Performance - Cash Generation - Prudent Growth Mirant’s estimated Federal NOL balance at December 31, 2009 was $2.7 billion An “ownership change” requires Mirant to reset  the limitation that determines how much annual taxable income may be offset by its NOLs in future years An ownership change occurs if there is an increase of more than 50 percentage points in the ownership of Mirant stock held by large Mirant shareholders from the date of a previous ownership change New limitation depends on Mirant stock value on the ownership change date and an interest rate determined by the IRS We expect that Mirant will experience an “ownership change” for federal income tax purposes  on the closing date of the proposed merger with RRI Energy RRI Energy has advised us that they expect RRI Energy to experience an ownership change on the closing date of the merger as well

21 Federal NOL Update (Cont.) Operational Performance - Cash Generation - Prudent Growth Assuming the shares of Mirant and RRI Energy are at or near current prices on the closing date of the proposed merger, Mirant expects that The combined company, GenOn Energy, will be unable to use any pre merger NOLs for the first 5 years following the merger Thereafter, assuming sufficient taxable income, GenOn will be able to use approximately $100MM – $125MM per year of pre merger NOLs until such NOLs expire Based on current commodity price forecasts, Mirant expects that GenOn Energy will pay only federal Alternative Minimum Tax and  certain state income taxes during the 5 years immediately following the merger Mirant‘s Board of Directors has extended its stockholder rights plan and the plan was approved at its 2010 Annual Meeting of Stockholders held on May 6, 2010 There is no assurance that the stockholder rights plan will prevent an ownership change prior to the closing date of the proposed merger

22 Additional Hedge Information Operational Performance - Cash Generation - Prudent Growth 1 Projected as of April 13, 2010 2 Power hedges include hedges with both power and natural gas 3 Realized Value of Hedges are nominal values and do not include certain adjustments required under fair value accounting ($millions) Q1 2010 Q1 2009 2010 2011 2012 2013 2014 Power 2 84 $    129 $  437 $  234 $  174 $  168 $  159 $  Fuel (15)      (21)      (61)      (31)      (34)     (10)     1         Realized Value of Hedges 69 $    108 $  376 $  203 $  140 $  158 $  160 $  Actual Projected 1,3 May-Dec 2010 2011 2012 2013 2.45 $          2.80 $          3.32 $          3.28 $          Average contract price of hedged coal before delivery ($/mmBtu)

23 Quarterly Generation by Dispatch Type Operational Performance - Cash Generation - Prudent Growth Net MW Net MWh Generated EAF (%) (1) Net Capacity Factor (%) Net MW Net MWh Generated EAF (%) (1) Net Capacity Factor (%) Baseload MidAtlantic 2,729 3,972,167 84.0 67.4 2,765 3,726,363 82.8 62.4 Northeast 238 364,410 96.4 70.9 238 365,210 94.6 71.1 California 0 0 Total Baseload 2,967 4,336,577 85.0 67.7 3,003 4,091,573 83.8 63.1 Intermediate MidAtlantic 1,400 54,692 37.4 1.8 1,400 104,373 35.1 3.5 Northeast 2,265 8,876 93.1 0.2 2,265 534,029 96.1 11.0 California 2,191 123,267 83.2 2.6 2,191 175,646 81.6 3.7 Total Intermediate 5,856 186,835 76.1 1.5 5,856 814,048 76.1 6.4 Peaking MidAtlantic 1,065 6,360 92.5 0.2 1,065 31,007 91.4 1.2 Northeast 32 386 92.6 0.6 32 306 97.9 0.5 California 156 (155) 96.1 0.0 156 232 92.6 0.1 Total Peaking 1,253 6,591 92.9 0.2 1,253 31,545 91.7 1.0 Total Mirant 10,076 4,530,003 81.0 20.5 10,112 4,937,166 80.5 22.3 (1) Equivalent Availability Factor - the total hours a unit is available in a period minus the sum of all full and partial outage equivalent expressed as a percent of all hours in a period. Generation by Dispatch Type First Quarter 2010 First Quarter 2009

24 Equivalent Forced Outage Rate (EFOR) EFOR  = Forced Outage Hours Forced Outage Hours + Service Hours Operational Performance - Cash Generation - Prudent Growth 2010 2009 Mid-Atlantic Baseload Coal 5% 10% Q1

25 Mirant Operations 10,076 MW Power plants sized by capacity Operational Performance - Cash Generation - Prudent Growth

26 Development Opportunities • Potential to add 2,500 – 3,500 MWs of capacity Entered into ten-year Power Purchase Agreement with PG&E for new 760 MW Marsh Landing Generating Station California Northeast Mid Atlantic • Potential to add 1,000 – 1,500 MWs of capacity • Potential to add 4,000 – 5,000 MWs of capacity Operational Performance - Cash Generation - Prudent Growth

27 Share Count (millions) Operational Performance - Cash Generation - Prudent Growth Weighted average shares outstanding - basic 145 145 Effect of dilutive securities 1 0 Weighted average shares outstanding - diluted 146 145 Shares outstanding at quarter end - basic 145 145 Effect of dilutive securities 1 0 Shares outstanding at end of quarter - diluted 146 145 March 31, 2009 Three Three Months Ending Months Ending March 31, 2010

28 Regulation G Reconciliation Operational Performance - Cash Generation - Prudent Growth (in millions except per share) Per Share 1 Per Share 1 Net Income 407 $       2.79 $         380 $       2.62 $         Unrealized gains (352) (2.41) (254) (1.75) Lower of cost or market inventory adjustments, net 3 0.02 (12) (0.08) Other 3 0.02 1 - Adjusted Net Income 61 $         0.42 $         115 $       0.79 $         Provision for income taxes - 8 Interest expense, net 50 36 Depreciation and amortization 51 36 Adjusted EBITDA 162 $       195 $       1 Per share amounts for 2010 are based on diluted weighted average shares outstanding of 146 million. Per share amounts for 2009 are based on diluted weighted average shares outstanding of 145 million. Table 1 Net Income to Adjusted Net Income and Adjusted EBITDA Quarter Ending Quarter Ending March 31, 2010 March 31, 2009

29 Regulation G Reconciliation (in millions) Mid- Atlantic Northeast California Other Operations Eliminations Total Net Income (Loss) 439 $       (2) $           2 $              (32) $            - $                 407 $        Unrealized (gains) losses (346)         4                 -                 (10)                -                    (352)          Lower of cost or market inventory adjustments, net 5               -                 -                 (2)                  -                    3                Other -               -                 -                 3                   -                    3                Adjusted Net Income (Loss) 98 $         2 $              2 $              (41) $            - $                 61 $          Interest expense, net 1               -                 -                 49                 -                    50             Depreciation and amortization 33            6                 8                 4                   -                    51             Adjusted EBITDA 132 $       8 $              10 $           12 $              - $                 162 $        Table 2 Adjusted Net Income (Loss) and Adjusted EBITDA Quarter Ending March 31, 2010 Operational Performance - Cash Generation - Prudent Growth

30 Regulation G Reconciliation (in millions) Mid- Atlantic Northeast California Other Operations Eliminations Total Net Income (Loss) 385 $       30 $           3 $               (39) $            1 $                   380 $      Unrealized (gains) losses (243)         (26)             -             15                 -                      (254)        Lower of cost or market inventory adjustments, net 4               (1)                1                  (16)                -                      (12)          Other -                1                 -                  -                   -                      1             Adjusted Net Income (Loss) 146 $       4 $              4 $               (40) $            1 $                   115 $      Provision for income taxes -                -                 -                  8                   -                      8             Interest expense, net 1               -                 1                  34                 -                      36           Depreciation and amortization 24            4                 5                  3                   -                      36           Adjusted EBITDA 171 $       8 $              10 $            5 $                1 $                   195 $      Table 3 Adjusted Net Income (Loss) and Adjusted EBITDA Quarter Ending March 31, 2009 Operational Performance - Cash Generation - Prudent Growth

31 Regulation G Reconciliation (in millions) Mid-Atlantic Northeast California Other Operations Eliminations Total        Energy 92 $                  (3) $          - $        21 $            - $            110 $              Contracted & capacity 89                     23            30            -               -                142                 Realized value of hedges 57                     12            -           -               -                69                   Realized gross margin 238                   32            30            21                -                321                 Unrealized gross margin 346                   (4)             -           10                -                352                 Gross margin 584 $                28 $         30 $         31 $            - $            673 $              (in millions) Mid-Atlantic Northeast California Other Operations Eliminations Total        Energy 72 $                  15 $         - $        27 $            (3) $               111 $              Contracted & capacity 85                     22            27            -               -                134                 Realized value of hedges 107                   1               -           -               -                108                 Realized gross margin 264                   38            27            27                (3)                  353                 Unrealized gross margin 243                   26            -           (15)               -                254                 Gross margin 507 $                64 $         27 $         12 $            (3) $               607 $              Gross Margin Quarter Ending March 31, 2010 Table 4 Quarter Ending  March 31, 2009 Operational Performance - Cash Generation - Prudent Growth

32 Regulation G Reconciliation (in millions) Gross margin 673 $                       607 $                      Unrealized gross margin (352)                         (254)                        Lower of cost or market inventory adjustments, net 3                              (12)                          Adjusted gross margin 324                          341                         Operations and maintenance expenses (166)                         (162)                        Lovett shutdown costs -                              1                             Merger-related costs 2                              -                              Adjusted operations and maintenance expenses (164)                         (161)                        Gain on sales of emissions allowances, net 2                              15                           Other, net (1)                             -                              Bankruptcy charges and legal contingencies 1                              -                              Adjusted EBITDA 162 $                       195 $                      Table 5 Gross Margin to Adjusted EBITDA Quarter  Ending Quarter  Ending March 31, 2010 March 31, 2009 Operational Performance - Cash Generation - Prudent Growth