<PAGE>   1

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                                 UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                ---------------

                                   FORM 10-Q
(Mark One)
[X]   QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d)
                  OF THE SECURITIES EXCHANGE ACT OF 1934

               FOR THE QUARTERLY PERIOD ENDED MARCH 31, 2001

                                       OR

[   ]   TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d)
                   OF THE SECURITIES EXCHANGE ACT OF 1934

           FOR THE TRANSITION PERIOD FROM           TO

                         COMMISSION FILE NUMBER 1-2745

                                ---------------

                          SOUTHERN NATURAL GAS COMPANY
             (Exact Name of Registrant as Specified in its Charter)

<TABLE>
<S>                                                 <C>
                     DELAWARE                                           63-0196650
          (State or Other Jurisdiction of                            (I.R.S. Employer
          Incorporation or Organization)                            Identification No.)
</TABLE>

<TABLE>
<S>                                                 <C>
                 EL PASO BUILDING
               1001 LOUISIANA STREET                                       77002
                  HOUSTON, TEXAS                                        (Zip Code)
     (Address of Principal Executive Offices)
</TABLE>

       Registrant's Telephone Number, Including Area Code: (713) 420-2600

     Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days. Yes [X]  No [ ]

     Indicate the number of shares outstanding of each of the issuer's classes
of common stock, as of the latest practicable date.

     Common stock, par value $3.75 per share. Shares outstanding on May 4, 2001:
1,000

     SOUTHERN NATURAL GAS COMPANY MEETS THE CONDITIONS OF GENERAL INSTRUCTION
H(1)(a) AND (b) OF FORM 10-Q AND IS THEREFORE FILING THIS REPORT WITH A REDUCED
DISCLOSURE FORMAT AS PERMITTED BY SUCH INSTRUCTION.

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                        PART I -- FINANCIAL INFORMATION

ITEM 1. FINANCIAL STATEMENTS

                          SOUTHERN NATURAL GAS COMPANY

                  CONDENSED CONSOLIDATED STATEMENTS OF INCOME
                                 (IN MILLIONS)
                                  (UNAUDITED)

<TABLE>
<CAPTION>
                                                              QUARTER ENDED
                                                                MARCH 31,
                                                              --------------
                                                              2001      2000
                                                              ----      ----
<S>                                                           <C>       <C>
Operating revenues..........................................  $111      $108
                                                              ----      ----
Operating expenses
  Operation and maintenance.................................    46        41
  Depreciation, depletion, and amortization.................    10         3
  Taxes, other than income taxes............................     6         5
                                                              ----      ----
                                                                62        49
                                                              ----      ----
Operating income............................................    49        59
                                                              ----      ----
Other income
  Earnings from unconsolidated affiliates...................     3         5
  Other, net................................................     3        (3)
                                                              ----      ----
                                                                 6         2
                                                              ----      ----
Income before interest, income taxes, and extraordinary
  items.....................................................    55        61
                                                              ----      ----
Non-affiliated interest and debt expense....................    11        10
Affiliated interest (income) expense, net...................    (4)        1
Income tax expense..........................................    18        19
                                                              ----      ----
                                                                25        30
                                                              ----      ----
Income before extraordinary items...........................    30        31
Extraordinary items, net of income taxes....................    --        12
                                                              ----      ----
Net income..................................................  $ 30      $ 43
                                                              ====      ====
</TABLE>

                            See accompanying notes.

                                        1
<PAGE>   3

                          SOUTHERN NATURAL GAS COMPANY

                     CONDENSED CONSOLIDATED BALANCE SHEETS
                      (IN MILLIONS, EXCEPT SHARE AMOUNTS)
                                  (UNAUDITED)

<TABLE>
<CAPTION>
                                                              MARCH 31,   DECEMBER 31,
                                                                2001          2000
                                                              ---------   ------------
<S>                                                           <C>         <C>
                                        ASSETS

Current assets
  Cash and cash equivalents.................................   $   --        $   --
  Accounts and notes receivable, net........................      496           297
  Materials and supplies....................................       15            15
  Other.....................................................       28            27
                                                               ------        ------
          Total current assets..............................      539           339
Property, plant, and equipment, net.........................    1,230         1,216
Investments in unconsolidated affiliates....................      108           105
Other.......................................................       27            12
                                                               ------        ------
          Total assets......................................   $1,904        $1,672
                                                               ======        ======

                         LIABILITIES AND STOCKHOLDER'S EQUITY

Current liabilities
  Accounts payable..........................................   $   45        $   50
  Current maturities of long-term debt......................      100           100
  Taxes payable.............................................      102            91
  Other.....................................................       28            28
                                                               ------        ------
          Total current liabilities.........................      275           269
                                                               ------        ------
Long-term debt, less current maturities.....................      598           399
                                                               ------        ------
Deferred income taxes.......................................      125           120
                                                               ------        ------
Other.......................................................       59            67
                                                               ------        ------
Commitments and contingencies
Stockholder's equity
  Common stock, par value $3.75 per share; authorized and
     issued 1,000 shares....................................       --            --
  Additional paid-in capital................................      102           102
  Retained earnings.........................................      745           715
                                                               ------        ------
          Total stockholder's equity........................      847           817
                                                               ------        ------
          Total liabilities and stockholder's equity........   $1,904        $1,672
                                                               ======        ======
</TABLE>

                            See accompanying notes.

                                        2
<PAGE>   4

                          SOUTHERN NATURAL GAS COMPANY

                CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS
                                 (IN MILLIONS)
                                  (UNAUDITED)

<TABLE>
<CAPTION>
                                                               QUARTER ENDED
                                                                 MARCH 31,
                                                              ---------------
                                                              2001       2000
                                                              -----      ----
<S>                                                           <C>        <C>
Cash flows from operating activities
  Net income................................................  $  30      $ 43
  Adjustments to reconcile net income to net cash from
     operating activities
     Depreciation, depletion, and amortization..............     10         3
     Extraordinary items....................................     --       (21)
     Deferred income tax expense............................      4         2
     Undistributed earnings of unconsolidated affiliates....     (3)       (5)
  Working capital changes, net of non-cash transactions.....     10        95
  Other.....................................................    (16)      (29)
                                                              -----      ----
          Net cash provided by operating activities.........     35        88
                                                              -----      ----
Cash flows from investing activities
  Purchases of property, plant, and equipment...............    (17)      (27)
  Net change in other affiliated advances receivable........   (225)      (66)
  Net proceeds from the sale of assets......................      7        74
                                                              -----      ----
          Net cash used in investing activities.............   (235)      (19)
                                                              -----      ----
Cash flows from financing activities
  Payments to retire long-term debt.........................   (100)       --
  Proceeds from the issuance of long-term debt..............    300        --
  Net change in other affiliated advances payable...........     --       (70)
                                                              -----      ----
          Net cash provided by (used in) financing
           activities.......................................    200       (70)
                                                              -----      ----
Net change in cash and cash equivalents.....................     --        (1)
Cash and cash equivalents
  Beginning of period.......................................     --         1
                                                              -----      ----
  End of period.............................................  $  --      $ --
                                                              =====      ====
</TABLE>

                            See accompanying notes.

                                        3
<PAGE>   5

                          SOUTHERN NATURAL GAS COMPANY

              NOTES TO CONDENSED CONSOLIDATED FINANCIAL STATEMENTS
                                  (UNAUDITED)

1. BASIS OF PRESENTATION


     Our 2000 Annual Report on Form 10-K includes a summary of our significant
accounting policies and other disclosures. You should read it in conjunction
with this Quarterly Report on Form 10-Q. The financial statements at March 31,
2001, and for the quarters ended March 31, 2001 and 2000, are unaudited. The
balance sheet at December 31, 2000, is derived from the audited financial
statements. These financial statements have been prepared pursuant to the rules
and regulations of the U.S. Securities and Exchange Commission and do not
include all disclosures required by accounting principles generally accepted in
the United States. In our opinion, we have made all adjustments, all of which
are of a normal, recurring nature, to fairly present our interim period results.
Information for interim periods may not necessarily indicate the results of
operations for the entire year due to the seasonal nature of our businesses. The
prior period information includes reclassifications which were made to conform
to the current presentation. These reclassifications have no effect on our
reported net income or stockholder's equity.


2. EXTRAORDINARY ITEMS

     During the first quarter of 2000, we sold Sea Robin Pipeline Company to
comply with a Federal Trade Commission (FTC) order related to our former parent
company's merger with El Paso Corporation. We received net proceeds of $71
million and recognized an extraordinary gain of $12 million, net of income taxes
of $9 million.

3. PROPERTY, PLANT, AND EQUIPMENT


     Our property, plant, and equipment consisted of the following:



<TABLE>
<CAPTION>
                                                              MARCH 31,   DECEMBER 31,
                                                                2001          2000
                                                              ---------   ------------
                                                                   (IN MILLIONS)
<S>                                                           <C>         <C>
Property, plant, and equipment, at cost.....................   $2,552        $2,529
Less accumulated depreciation, depletion, and
  amortization..............................................    1,322         1,313
                                                               ------        ------
          Total property, plant, and equipment, net.........   $1,230        $1,216
                                                               ======        ======
</TABLE>


4. DEBT AND OTHER CREDIT FACILITIES


     In February 2001, we issued $300 million aggregate principal amount 7.35%
Notes due 2031. Proceeds of approximately $297 million, net of issuance costs,
were used to pay off $100 million of our 8.875% Notes due 2001 and for general
corporate purposes.


5. COMMITMENTS AND CONTINGENCIES

  Legal Proceedings


     In 1997, we were named a defendant in actions brought by Jack Grynberg on
behalf of the U.S. Government under the False Claims Act. Generally, these
complaints allege an industry-wide conspiracy to under report the heating value
as well as the volumes of the natural gas produced from federal and Native
American lands, which deprived the U.S. Government of royalties. These matters
have been consolidated for pretrial purposes (In re: Natural Gas Royalties Qui
Tam Litigation, U.S. District Court for the District of Wyoming).



     We were named a defendant in Quinque Operating Company, et al v. Gas
Pipelines and Their Predecessors, et al, filed in 1999 in the District Court of
Stevens County, Kansas. This class action complaint alleges that the defendants
mismeasured natural gas volumes and heating content of natural gas on


                                        4
<PAGE>   6


non-federal and non-Native American lands. The Quinque complaint was transferred
to the same court handling the Grynberg complaint, and has now been sent back to
Kansas State Court for further proceedings.


     We are also a named defendant in numerous lawsuits and a named party in
numerous governmental proceedings arising in the ordinary course of our
business.

     While the outcome of the matters discussed above cannot be predicted with
certainty, we do not expect the ultimate resolution of these matters will have a
material adverse effect on our financial position, operating results, or cash
flows.

  Environmental


     We are subject to extensive federal, state, and local laws and regulations
governing environmental quality and pollution control. These laws and
regulations require us to remove or remedy the effect on the environment of the
disposal or release of specified substances at current and former operating
sites. As of March 31, 2001, we had a reserve of approximately $14 million for
expected remediation costs. In addition, we expect to make capital expenditures
for environmental matters of approximately $7 million in the aggregate for the
years 2001 through 2006. These expenditures primarily relate to compliance with
air regulations.



     It is possible that new information or future developments could require us
to reassess our potential exposure related to environmental matters. We may
incur significant costs and liabilities in order to comply with existing
environmental laws and regulations. It is also possible that other developments,
such as increasingly strict environmental laws and regulations and claims for
damages to property, employees, other persons and the environment resulting from
our current or past operations, could result in substantial costs and
liabilities in the future. As this information becomes available, or other
relevant developments occur, we will adjust our accrual amounts accordingly.
While there are still uncertainties relating to the ultimate costs we may incur,
based upon our evaluation and experience to date, we believe the recorded
reserves are adequate.


  Rates and Regulatory Matters


     In March 2000, the Federal Energy Regulatory Commission (FERC) issued an
order requested by Southern LNG Inc., our wholly owned subsidiary, which
authorized the recommissioning of Southern LNG's Elba Island receiving terminal
near Savannah, Georgia. In August 2000, Southern LNG filed an application with
FERC requesting limited amendment to the certificate issued in March 2000 which
would expand the throughput capability of the Elba Island terminal. The
estimated cost of the project is approximately $52 million with an anticipated
in-service date of October 2001. FERC issued a preliminary determination on
non-environmental issues in February 2001.



     In May 2000, we filed an application with FERC to expand our pipeline
system by 336 million cubic feet of natural gas per day, to serve new power
generation loads, being sited by Southern Company Services in Alabama at an
estimated cost of $141 million. Phase I of the project is expected to be in
service in June 2002, and Phase II is expected to be in service in June 2003. We
received a certificate order from FERC in March 2001.



     In April 2001, we filed an application with FERC to expand our north main
line pipeline system to supply transportation demand services to a simple cycle
electric power generation plant in Calhoun County, Alabama, for the summer
months, and Alagasco, one of our customers, and the City of Sylacauga during the
winter months. This additional capacity to provide these services will be
created through a combination of construction of new looping lines, replacement
or uprating of existing pipe, and installation of added compression. The
estimated cost of the project is approximately $26 million with an anticipated
in-service date of June 2003.



     Also in April 2001, we filed an application with FERC seeking authorization
to construct and operate the Cypress Pipeline system in Southeastern Georgia and
Florida for an estimated cost of $240 million. This 166-mile pipeline will be
capable of transporting 310 million cubic feet of natural gas per day from our
liquefied natural gas receiving terminal at Elba Island in Savannah, Georgia to
interconnections with our South Georgia Lateral; Florida Gas Transmission
Company (a jointly owned subsidiary of El Paso and Enron

                                        5
<PAGE>   7

Corporation); Atlanta Gas Light near Brunswick, Georgia; and Jacksonville
Electric Authority's new Brandy Branch generating plant near Jacksonville,
Florida. Construction is scheduled to begin in the third quarter of 2002, and
the pipeline's projected in-service date is June 1, 2003.

6. TRANSACTIONS WITH RELATED PARTIES

     We participate in El Paso's cash management program which matches
short-term cash excesses and requirements of participating affiliates, thus
minimizing total borrowing from outside sources. We had advanced $432 million at
March 31, 2001, at a market rate of interest which was 5.58% at March 31, 2001.
At December 31, 2000, we had advanced $208 million.

                                        6
<PAGE>   8

ITEM 2. MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS
        OF OPERATIONS

     The information contained in Item 2 updates, and you should read it in
conjunction with, information disclosed in Part II, Items 7, 7A, and 8, in our
Annual Report on Form 10-K for the year ended December 31, 2000, in addition to
the financial statements and notes presented in Item 1 of this Quarterly Report
on Form 10-Q.

                             RESULTS OF OPERATIONS

     During the first quarter of 2000, we completed our sale of Sea Robin
Pipeline Company to comply with an FTC order related to our former parent
company's merger with El Paso. Net proceeds from this sale were $71 million and
we recognized an extraordinary gain of $12 million, net of income taxes of $9
million.

     Below are the operating results and an analysis of those results for each
of the quarters ended March 31:

<TABLE>
<CAPTION>
                                                                2001        2000
                                                              --------    --------
                                                              (IN MILLIONS, EXCEPT
                                                                VOLUME AMOUNTS)
<S>                                                           <C>         <C>
Operating revenues..........................................   $  111      $  108
Operating expenses..........................................      (62)        (49)
Other income, net...........................................        6           2
                                                               ------      ------
  Earnings before interest expense and income taxes.........   $   55      $   61
                                                               ======      ======
Throughput volumes (BBtu/d)(1)..............................    2,231       2,813
                                                               ======      ======
</TABLE>

---------------
(1) BBtu/d means billion British thermal units per day.

     In March 2000, FERC issued an order allowing us to reactivate our Elba
Island liquefied natural gas facility. Following the reactivation, we made
adjustments that were previously approved under a FERC order, including
re-establishing costs related to the facility, which we were previously ordered
to write off, and eliminating a regulatory asset for future recoveries of our
Elba Island facility costs. As of January 1, 2000, we also stopped recovering
amounts under a minimum bill provision under a prior settlement order.

     Operating revenues for the quarter ended March 31, 2001, were $3 million
higher than the same period in 2000. The increase was due to higher prices on
sales of excess fuel recoveries in the first quarter of 2001. Partially
offsetting the increase were lower transportation revenues from the sale of our
Sea Robin system, lower rates following our rate case settlement, and the
elimination of the minimum bill provisions on our Elba Island facility that FERC
approved for reactivation, all occurring in March of 2000.

     Operating expenses for the quarter ended March 31, 2001, were $13 million
higher than the same period in 2000. The increase was due to higher fuel costs
resulting from higher gas prices in the first quarter of 2001 and the favorable
impact on depreciation expense of the FERC's authorization to reactivate our
Elba Island facility in the first quarter of 2000. The increase was partially
offset by lower overhead allocations in the first quarter of 2001 and lower
depreciation expense following our 2000 rate case settlement.

     Other income for the quarter ended March 31, 2001, was $4 million higher
than the same period in 2000. The increase was due to the elimination of an
asset for the future recovery of costs established for the Elba Island facility
in the first quarter of 2000 and contract termination fees in the first quarter
of 2001 which were partially offset by lower equity earnings resulting from the
sale of our one-third interest in Destin Pipeline Company in the first quarter
of 2000.

                                        7
<PAGE>   9

NON-AFFILIATED INTEREST AND DEBT EXPENSE

     Non-affiliated interest and debt expense for the quarter ended March 31,
2001, was $1 million higher than 2000 due to increased long-term borrowings in
the first quarter of 2001 for operating requirements and retirement of a portion
of our long-term borrowings due in 2001.

AFFILIATED INTEREST INCOME, NET

     Affiliated interest income, net for the first quarter ended March 31, 2001,
was $5 million higher than 2000 due to increased average advances to El Paso in
2001.

INCOME TAX EXPENSE

     The income tax expense for the quarters ended March 31, 2001 and 2000, was
$18 million and $19 million, resulting in an effective tax rate of 38 percent
for both periods. Our effective tax rates were higher than the statutory rate of
35 percent primarily due to state income taxes.

OTHER

     For discussion of our expansion activities, see Part I, Financial
Information, Note 5.

                                        8
<PAGE>   10

CAUTIONARY STATEMENT FOR PURPOSES OF THE "SAFE HARBOR" PROVISIONS OF THE PRIVATE
                    SECURITIES LITIGATION REFORM ACT OF 1995

     This report contains or incorporates by reference forward-looking
statements within the meaning of the Private Securities Litigation Reform Act of
1995. Where any forward-looking statement includes a statement of the
assumptions or bases underlying the forward-looking statement, we caution that,
while we believe these assumptions or bases to be reasonable and to be made in
good faith, assumed facts or bases almost always vary from the actual results,
and the differences between assumed facts or bases and actual results can be
material, depending upon the circumstances. Where, in any forward-looking
statement, we or our management express an expectation or belief as to future
results, that expectation or belief is expressed in good faith and is believed
to have a reasonable basis. We cannot assure you, however, that the statement of
expectation or belief will result or be achieved or accomplished. The words
"believe," "expect," "estimate," "anticipate" and similar expressions will
generally identify forward-looking statements.

ITEM 3. QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK

     This information updates, and you should read it in conjunction with,
information disclosed in Part II, Item 7A in our Annual Report on Form 10-K for
the year ended December 31, 2000, in addition to the information presented in
Items 1 and 2 of this Quarterly Report on Form 10-Q.

     There are no material changes in our quantitative and qualitative
disclosures about market risks from those reported in our Annual Report on Form
10-K for the year ended December 31, 2000.

                                        9
<PAGE>   11

                          PART II -- OTHER INFORMATION

ITEM 1. LEGAL PROCEEDINGS

     See Part I, Financial Information, Note 5, which is incorporated by
reference herein.

ITEM 2. CHANGES IN SECURITIES AND USE OF PROCEEDS

     None.

ITEM 3. DEFAULTS UPON SENIOR SECURITIES

     None.

ITEM 4. SUBMISSION OF MATTERS TO A VOTE OF SECURITY-HOLDERS

     None.

ITEM 5. OTHER INFORMATION

     None.

ITEM 6. EXHIBITS AND REPORTS ON FORM 8-K

a. Exhibits

     None.

     Undertaking

          We hereby undertake, pursuant to Regulation S-K, Item 601(b),
     paragraph (4)(iii), to furnish to the U.S. Securities and Exchange
     Commission, upon request, all constituent instruments defining the rights
     of holders of our long-term debt not filed herewith for the reason that the
     total amount of securities authorized under any of such instruments does
     not exceed 10 percent of our total consolidated assets.

b. Reports on Form 8-K

     - We filed a current report on Form 8-K, dated February 6, 2001, announcing
       we declared and paid a dividend on our common stock in the amount of
       $100,000,000 on December 28, 2000.

     - We filed a current report on Form 8-K, dated February 14, 2001,
       announcing we issued $300 million aggregate principal amount of 7.35%
       Notes due February 15, 2031.

                                        10
<PAGE>   12

                                   SIGNATURES

     Pursuant to the requirements of the Securities Exchange Act of 1934, the
registrant has duly caused this report to be signed on its behalf by the
undersigned thereunto duly authorized.

                                            SOUTHERN NATURAL GAS COMPANY

Date: May 11, 2001                                 /s/ GREG G. GRUBER
                                                       Greg G. Gruber
                                                   Senior Vice President
                                                and Chief Financial Officer

Date: May 11, 2001                                /s/ JEFFREY I. BEASON
                                                     Jeffrey I. Beason
                                            Senior Vice President and Controller
                                                 (Chief Accounting Officer)

                                        11