SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                  SCHEDULE 13G
                                  Rule 13d-102

                   Under the Securities Exchange Act of 1934
                              (Amendment No. __)*

                                UAL Corporation
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                                (Name of Issuer)

                                  Common Stock
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                         (Title of Class of Securities)

                                   902549807
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                                 (CUSIP Number)

                                   12/31/2007
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            (Date of Event which Requires Filing of this Statement)

      Check the appropriate 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)

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      * 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
securities, and for any subsequent amendment containing information which
would alter disclosures provided in a prior cover page.

      The information required on 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).

Page 1 of 6 Pages

<PAGE>

CUSIP No. 902549807
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(1) Names of reporting persons.

    LMM LLC
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(2) Check the appropriate box if a member of a group (see instructions)   (a)|X|
                                                                          (b)|_|
--------------------------------------------------------------------------------
(3) SEC use only.

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(4) Citizenship or place of organization.

    Delaware
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Number of shares beneficially owned by each reporting person with:

    (5) Sole voting power:
        -0-

    (6) Shared voting power:
        8,900,000

    (7) Sole dispositive power:
        -0-

    (8) Shared dispositive power:
        8,900,000

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(9) Aggregate amount beneficially owned by each reporting person.

    8,900,000
--------------------------------------------------------------------------------
(10) Check if the aggregate amount in Row (9) excludes certain shares       |_|
     (see instructions).
--------------------------------------------------------------------------------
(11) Percent of class represented by amount in Row 9.

     7.65%
--------------------------------------------------------------------------------
(12) Type of reporting person (see instructions).

     IA    OO
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Page 2 of 6 Pages

<PAGE>

CUSIP No. 902549807
--------------------------------------------------------------------------------
(1) Names of reporting persons.

    Legg Mason Opportunity Trust
--------------------------------------------------------------------------------
(2) Check the appropriate box if a member of a group (see instructions)   (a)|_|
                                                                          (b)|_|
--------------------------------------------------------------------------------
(3) SEC use only.

--------------------------------------------------------------------------------
(4) Citizenship or place of organization.

    Maryland
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Number of shares beneficially owned by each reporting person with:

    (5) Sole voting power:
        -0-

    (6) Shared voting power:
        8,900,000

    (7) Sole dispositive power:
        -0-

    (8) Shared dispositive power:
        8,900,000

--------------------------------------------------------------------------------
(9) Aggregate amount beneficially owned by each reporting person.

    8,900,000
--------------------------------------------------------------------------------
(10) Check if the aggregate amount in Row (9) excludes certain shares       |_|
     (see instructions).
--------------------------------------------------------------------------------
(11) Percent of class represented by amount in Row 9.

     7.65%
--------------------------------------------------------------------------------
(12) Type of reporting person (see instructions).

     IV      OO
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Page 3 of 6 Pages

<PAGE>

CUSIP No. 902549807
--------------------------------------------------------------------------------
(1) Names of reporting persons.

    Legg Mason Capital Management, Inc.
--------------------------------------------------------------------------------
(2) Check the appropriate box if a member of a group (see instructions)   (a)|X|
                                                                          (b)|_|
--------------------------------------------------------------------------------
(3) SEC use only.

--------------------------------------------------------------------------------
(4) Citizenship or place of organization.

    Maryland
--------------------------------------------------------------------------------
Number of shares beneficially owned by each reporting person with:

    (5) Sole voting power:
        -0-

    (6) Shared voting power:
        1,276,434

    (7) Sole dispositive power:
        -0-

    (8) Shared dispositive power:
        1,276,434

--------------------------------------------------------------------------------
(9) Aggregate amount beneficially owned by each reporting person.

    1,276,434
--------------------------------------------------------------------------------
(10) Check if the aggregate amount in Row (9) excludes certain shares       |_|
     (see instructions).
--------------------------------------------------------------------------------
(11) Percent of class represented by amount in Row 9.

     1.10%
--------------------------------------------------------------------------------
(12) Type of reporting person (see instructions).

     CO     IA
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Page 4 of 6 Pages

<PAGE>

Item 1(a). Name of Issuer:

           UAL Corporation

Item 1(b). Address of Issuer's Principal Executive Offices:

           77 W. Wacker
           Chicago, IL 600601

Item 2(a). Name of Person Filing:

           LMM LLC
           Legg Mason Opportunity Trust
           Legg Mason Capital Management, Inc.

Item 2(b). Address or Principal Business Office or, If None, Residence:

           100 Light Street 
           Baltimore, MD 21202

Item 2(c). Citizenship:

           Maryland, Delaware

Item 2(d). Title of Class of Securities:

           Common Stock

Item 2(e). CUSIP No.:

           902549807

Item 3. If This Statement is Filed Pursuant to Rule 13d-1(b), or 13d-2(b) or
        (c), Check Whether the Person Filing is a:

        (a) |_| Broker or dealer registered under section 15 of the Act
                (15 U.S.C. 78o).

        (b) |_| Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c).

        (c) |_| Insurance company as defined in section 3(a)(19) of the Act
                (15 U.S.C. 78c).

        (d) |_| Investment company registered under section 8 of the Investment
                Company Act of 1940 (15 U.S.C 80a-8).

        (e) |_| An investment adviser in accordance with
                ss. 240.13d-1(b)(1)(ii)(E);

        (f) |_| An employee benefit plan or endowment fund in accordance with
                ss.240.13d-1(b)(1)(ii)(F);

        (g) |_| A parent holding company or control person in accordance with
                ss.240.13d- 1(b)(1)(ii)(G);

        (h) |_| A savings associations as defined in Section 3(b) of the
                Federal Deposit Insurance Act (12 U.S.C. 1813);

        (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 (15 U.S.C. 80a-3);

        (j) |X| Group, in accordance with ss. 240.13d-1(b)(1)(ii)(J).

        If this statement is filed pursuant to Rule 13d-1(c),
        check this box. |_|

Item 4. Ownership 

    (a) Amount beneficially owned:
        10,176,434

    (b) Percent of class:
        8.75%

    (c) Number of shares as to which such person has:
        (i)   Sole power to direct the vote
              -0-

        (ii)  Shared power to direct the vote
              10,176,434

        (iii) Sole power to dispose or direct the disposition of
              -0-

        (iv)  Shared power to dispose or direct the disposition of
              10,176,434

Item 5. Ownership of 5 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 5 percent of the class of  securities, check the following |_|

Item 6. Ownership of More than 5 Percent on Behalf of Another Person.

        Various accounts managed by the investment advisers identified in Item 8
        have the right to receive or the power to direct the receipt of
        dividends from, or the proceeds from the sale of shares of the issuer.  
        
        The interest of one account, Legg Mason Opportunity Trust, a portfolio
        of Legg Mason Investment Trust, Inc. an investment company registered
        under the Investment Company Act of 1940 and managed by LMM LLC,
        amounted to 8,900,000 shares or 7.65% of the total shares outstanding.

Item 7. Identification and Classification of the Subsidiary Which Acquired the 
        Security Being Reported on by the Parent Holding Company or Control 
        Person.

        n/a

Item 8. Identification and Classification of Members of the Group.

        LMM LLC - investment adviser
        Legg Mason Capital Management, Inc. - investment adviser


Item 9. Notice of Dissolution of Group.

        n/a

Item 10. Certifications

         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 the securities and were not acquired and are
         not held in connection with or as a participant in any transaction
         having that purpose or effect.

Page 5 of 6 Pages

<PAGE>

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.

                                      LMM LLC

Date: 02/14/2008                      /s/ Nicholas C. Milano
                                      Name:  Nicholas C. Milano
                                      Title: Chief Compliance Officer


                                      Legg Mason Capital Management, Inc.

Date: 02/14/2008                      /s/ Nicholas C. Milano
                                      Name:  Nicholas C. Milano
                                      Title: Chief Compliance Officer


The original statement shall be signed by each person on whose behalf the
statement is filed or his authorized representative. If the statement is signed
on behalf of a person by his authorized representative other than an executive
officer or general partner of the filing person, evidence of the
representative's authority to sign on behalf of such person shall be filed with
the statement, Provided, however, That a power of attorney for this purpose
which is already on file with the Commission may be incor porated by reference.
The name and any title of each person who signs the statement shall be typed or
printed beneath his signature.

ATTENTION: Intentional misstatements or omissions of fact constitute Federal
criminal violations (see 18 U.S.C. 1001). (Secs. 3(b), 13(d)(1), 13(d)(2),
13(d)(5),  13(d)(6), 13(g)(1), 13(g)(2), 13(g)(5), 23, 48 Stat. 882, 894, 901;
sec. 203(a),  49 Stat. 704; sec. 8, 49 Stat. 1379; sec. 10, 78 Stat. 88a; sec.
2, 82 Stat. 454;  secs. 1, 2, 84 Stat. 1497; secs. 3, 10, 18, 89 Stat. 97, 119,
155; secs. 202, 203,  91 Stat. 1494, 1498, 1499; (15 U.S.C. 78c(b), 78m(d)(1),
78m(d)(2), 78m(d)(5),  78m(d)(6), 78m(g)(1), 78m(g)(2), 78m(g)(5), 78w)) [43 FR
18499, Apr. 28, 1978,  as amended at 43 FR 55756, Nov. 29, 1978; 44 FR 2148,
Jan. 9, 1979; 44 FR 11751,  Mar. 2, 1979; 61 FR 49959, Sept. 24, 1996; 62 FR
35340, July 1, 1997; 63 FR 2867,  Jan. 16, 1998; 63 FR 15287, Mar. 31, 1998]

Page 6 of 6 Pages





This Joint Filing Agreement confirms the agreement by and among the undersigned
that the Schedule 13G is filed on behalf of each of the reporting person(s)
identified below.

LMM LLC


By:_____/s/_Nicholas C. Milano____________________________
        Nicholas C. Milano, Chief Compliance Officer

Legg Mason Opportunity Trust,
a portfolio of Legg Mason Investment Trust, Inc.


By:___/s/_Gregory T. Merz_________________________________
      Gregory T. Merz, Vice President

Legg Mason Capital Management, Inc.


By:_____/s/_Nicholas C. Milano____________________________
        Nicholas C. Milano, Chief Compliance Officer