<PAGE>   1

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

                                 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 SEPTEMBER 30, 2000

                                       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 1-2700
                             ---------------------
                          EL PASO NATURAL GAS COMPANY
             (Exact Name of Registrant as Specified in its Charter)

<TABLE>
<S>                                            <C>
                   DELAWARE                                      74-0608280
         (State or Other Jurisdiction                         (I.R.S. Employer
      of Incorporation or Organization)                     Identification No.)
           EL PASO ENERGY BUILDING
            1001 LOUISIANA STREET
                HOUSTON, TEXAS                                     77002
   (Address of Principal Executive Offices)                      (Zip Code)
</TABLE>

       Registrant's Telephone Number, Including Area Code: (713) 420-2131

     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 $1.00 per share. Shares outstanding on November 6,
2000: 1,000

     EL PASO 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.
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
<PAGE>   2

                        PART I -- FINANCIAL INFORMATION

ITEM 1. FINANCIAL STATEMENTS

                          EL PASO NATURAL GAS COMPANY

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

<TABLE>
<CAPTION>
                                                                 QUARTER         NINE MONTHS
                                                                  ENDED             ENDED
                                                              SEPTEMBER 30,     SEPTEMBER 30,
                                                              --------------    --------------
                                                              2000     1999     2000     1999
                                                              -----    -----    -----    -----
<S>                                                           <C>      <C>      <C>      <C>
Operating revenues..........................................  $121     $120     $356     $359
                                                              ----     ----     ----     ----
Operating expenses
  Operation and maintenance.................................    36       44      117      126
  Depreciation, depletion, and amortization.................    17       16       50       47
  Taxes, other than income taxes............................     7        7       22       23
                                                              ----     ----     ----     ----
                                                                60       67      189      196
                                                              ----     ----     ----     ----
Operating income............................................    61       53      167      163
                                                              ----     ----     ----     ----
Other income, net...........................................     3        1        3        1
                                                              ----     ----     ----     ----
Income before interest and income taxes.....................    64       54      170      164
                                                              ----     ----     ----     ----
Non-affiliated interest and debt expense....................    21       24       71       79
Affiliated interest income, net.............................   (17)     (17)     (56)     (45)
Income tax expense..........................................    23       18       60       50
                                                              ----     ----     ----     ----
                                                                27       25       75       84
                                                              ----     ----     ----     ----
Net income..................................................  $ 37     $ 29     $ 95     $ 80
                                                              ====     ====     ====     ====
</TABLE>

                            See accompanying notes.

                                        1
<PAGE>   3

                          EL PASO NATURAL GAS COMPANY

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

<TABLE>
<CAPTION>
                                                              SEPTEMBER 30,   DECEMBER 31,
                                                                  2000            1999
                                                              -------------   ------------
<S>                                                           <C>             <C>
                                          ASSETS
Current assets
  Cash and cash equivalents.................................     $   --          $   --
  Accounts and notes receivable, net........................      1,058           1,414
  Materials and supplies....................................         32              28
  Other.....................................................          3               9
                                                                 ------          ------
          Total current assets..............................      1,093           1,451
Property, plant, and equipment, net.........................      1,682           1,532
Other.......................................................        115             117
                                                                 ------          ------
          Total assets......................................     $2,890          $3,100
                                                                 ======          ======

                           LIABILITIES AND STOCKHOLDER'S EQUITY
Current liabilities
  Accounts payable..........................................     $   78          $   65
  Short-term borrowings.....................................        186             567
  Taxes payable.............................................         97              77
  Other.....................................................        103              67
                                                                 ------          ------
          Total current liabilities.........................        464             776
Long-term debt, less current maturities.....................        882             873
Deferred income taxes.......................................        223             172
Other.......................................................        121             153
Commitments and contingencies
Stockholder's equity
  Preferred stock, 1,000,000 shares authorized; 8% par value
     $0.01 per share; 500,000 shares issued; stated at
     liquidation value......................................        350             350
  Common stock, par value $1 per share; authorized and
     issued
     1,000 shares...........................................         --              --
  Additional paid-in capital................................        700             700
  Retained earnings.........................................        150              76
                                                                 ------          ------
          Total stockholder's equity........................      1,200           1,126
                                                                 ------          ------
          Total liabilities and stockholder's equity........     $2,890          $3,100
                                                                 ======          ======
</TABLE>

                            See accompanying notes.

                                        2
<PAGE>   4

                          EL PASO NATURAL GAS COMPANY

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

<TABLE>
<CAPTION>
                                                               NINE MONTHS
                                                                  ENDED
                                                              SEPTEMBER 30,
                                                              --------------
                                                              2000     1999
                                                              -----    -----
<S>                                                           <C>      <C>
Cash flows from operating activities
  Net income................................................  $  95    $  80
  Adjustments to reconcile net income to net cash from
     operating activities
     Depreciation, depletion, and amortization..............     50       47
     Deferred income tax expense............................     25       17
     Gain on sale of assets.................................     (3)      --
     Risk-sharing revenue...................................    (23)     (23)
  Working capital changes, net of non-cash transactions.....     (7)     137
  Other.....................................................      3       (7)
                                                              -----    -----
          Net cash provided by operating activities.........    140      251
                                                              -----    -----
Cash flows from investing activities
  Purchases of property, plant, and equipment...............   (179)     (36)
  Net change in other affiliated advances...................    382     (138)
  Proceeds from the sale of assets..........................     36       --
  Other.....................................................      4        2
                                                              -----    -----
          Net cash provided by (used in) investing
           activities.......................................    243     (172)
                                                              -----    -----
Cash flows from financing activities
  Net borrowings (repayments) of commercial paper...........   (382)      20
  Revolving credit borrowings...............................    175      382
  Revolving credit repayments...............................   (175)    (422)
  Payments to retire long-term debt.........................     (1)     (58)
                                                              -----    -----
          Net cash used in financing activities.............   (383)     (78)
                                                              -----    -----
Increase in cash and cash equivalents.......................     --        1
Cash and cash equivalents
          Beginning of period...............................     --        9
                                                              -----    -----
          End of period.....................................  $  --    $  10
                                                              =====    =====
</TABLE>

                            See accompanying notes.

                                        3
<PAGE>   5

                          EL PASO NATURAL GAS COMPANY

              NOTES TO CONDENSED CONSOLIDATED FINANCIAL STATEMENTS
                                  (UNAUDITED)

1. BASIS OF PRESENTATION

     Our 1999 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 condensed consolidated financial
statements at September 30, 2000, and for the quarters and nine months ended
September 30, 2000 and 1999, are unaudited. The condensed consolidated balance
sheet at December 31, 1999, 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. ACQUISITIONS

     In March 2000, we purchased the All American Pipeline, a crude oil
transportation system, for $129 million. The system consists of 1,088 miles of
pipeline which runs from McCamey, Texas to Emidio Station near Bakersfield,
California. We intend to convert the non-California portion of the oil pipeline
to a natural gas pipeline, pending approval from the Federal Energy Regulatory
Commission (FERC).

3. PROPERTY, PLANT, AND EQUIPMENT

     Our property, plant, and equipment consisted of the following at September
30, 2000 and December 31, 1999:

<TABLE>
<CAPTION>
                                                               2000      1999
                                                              ------    ------
                                                               (IN MILLIONS)
<S>                                                           <C>       <C>
Property, plant, and equipment, at cost.....................  $2,629    $2,448
Less accumulated depreciation...............................   1,023       994
                                                              ------    ------
                                                               1,606     1,454
Additional acquisition cost assigned to utility plant, net
  of accumulated amortization...............................      76        78
                                                              ------    ------
          Total property, plant, and equipment, net.........  $1,682    $1,532
                                                              ======    ======
</TABLE>

4. DEBT AND OTHER CREDIT FACILITIES

     In August 2000, El Paso Energy replaced its $1,250 million 364-day
renewable revolving credit and competitive advance facility, with a $2 billion
facility, and its $750 million 3-year revolving credit and competitive advance
facility, with a $1 billion facility. We are a designated borrower under these
new facilities. Our interest rate for these facilities varies and would have
been LIBOR plus 41 basis points as of September 30, 2000. The available credit
under these facilities is expected to be used for El Paso Energy's general
corporate purposes including, but not limited to, supporting our commercial
paper program.

                                        4
<PAGE>   6

     At September 30, 2000, our weighted average interest rate on short-term
borrowings was 6.9% and at December 31, 1999, it was 6.6%. We had the following
short-term borrowings at September 30, 2000 and December 31, 1999:

<TABLE>
<CAPTION>
                                                              2000     1999
                                                              -----    ----
                                                              (IN MILLIONS)
<S>                                                           <C>      <C>
Commercial paper............................................  $ 186    $567
                                                              =====    ====
</TABLE>

     In October 2000, El Paso Energy issued $300 million aggregate principal
amount 8.05% medium-term notes due 2030. From the proceeds of this transaction,
$110 million was transferred to us and we repaid a portion of our commercial
paper borrowings.

     For the nine months ended September 30, 2000, we accrued $24 million in
dividends payable on our 8% preferred stock.

5. COMMITMENTS AND CONTINGENCIES

  Rates and Regulatory Matters

     As of September 30, 2000, we have 27 percent of our capacity subscribed
under shorter-term contracts. Currently, we are aggressively pursuing the
renegotiation and renewal of expiring contracts, and the sale of excess capacity
under firm transportation arrangements. However, we are uncertain if future
contracts will be on terms as favorable to us as those that currently exist.
Also, customers and other groups may dispute new and renewed contracts. As a
result, we cannot be sure that regulators or other jurisdictional bodies will
not intercede in our re-contracting process and alter the ultimate outcome of
our efforts.

     In June 1995, we filed new system rates for our mainline transportation
with the FERC. In April 1997, FERC approved our settlement to resolve this
proceeding as well as issues surrounding certain contract reductions and
expirations that occurred from January 1, 1996 through December 31, 1997. FERC
also determined that Southern California Edison Company (Edison) should have its
rates separately determined. The settlement was effective as of January 1, 1996.

     In November 1999, FERC approved the joint settlement between us and Edison
and reapproved our rate settlement conditioned upon the immediate adjustment of
our fuel charges for several facilities refunctionalized as gathering. Following
FERC's action, we filed for rehearing of FERC's fuel adjustment requirement.
FERC denied the request for rehearing and required that the fuel adjustment be
implemented effective February 1, 2000. In June 2000, we implemented the
settlement and paid Edison $35 million, including interest for the period
January 1, 1998 through June 30, 1999. In July 2000, we began charging Edison
the lower settlement rates and fuel charges. On August 1, 2000, a final rate
refund for the period July 1, 1999 through June 30, 2000 was made in the amount
of $3.6 million.

     Our rate settlement establishes, among other things, base rates through
December 31, 2005. According to the settlement, our base rates began escalating
annually in 1998 as a result of inflationary factors. We have the right to
increase or decrease base rates if changes in laws or regulations result in
increased or decreased costs in excess of $10 million a year. In addition, all
of our settling customers participate in risk sharing provisions under our rate
case settlement. Under these provisions, we received and continue to receive
cash payments totaling $295 million for a portion of the risk we assumed from
certain capacity relinquishments by our customers at the end of 1997. The cash
received is deferred, and we recognize this deferral in revenues ratably over
the risk sharing period. As of September 30, 2000, we had unearned risk sharing
revenues of approximately $104 million and had $43 million remaining to be
collected from customers under this provision. If the revenues from remarketing
our relinquished capacity to customers exceeds certain dollar levels specified
in the rate settlement, we are obligated to refund a portion of the excess to
customers. Under this provision, we refunded $15 million for 1999 revenues to
customers and, as of September 30, 2000, have reserved $9 million against 2000
revenues. Both risk and revenue sharing provisions of the rate settlement extend
through 2003.

                                        5
<PAGE>   7

     In 1998, we transferred our Chaco Station to El Paso Field Services to
comply with a FERC ruling that this asset should be functionalized as a
gathering rather than a transmission facility. In October 1999, the Court of
Appeals sustained FERC's determination, but remanded to FERC issues relating to
the appropriate fuel and rate treatment resulting from its refunctionalization.
In August 1999, a complaint was filed seeking a determination that our Blanco
Compressor Station is a non-jurisdictional gathering facility rather than a
jurisdictional transmission facility. In a November 1999 order, FERC ruled that
two of the three Blanco compressor facilities were gathering facilities, and
that an immediate adjustment of our fuel charges to eliminate the effects of the
refunctionalized facilities was appropriate, but that no change should be made
to our base rates as a result of refunctionalization. In April 2000, FERC denied
our request for rehearing and ordered us to adjust our fuel charges effective
February 1, 2000. We have implemented this order and, as of September 2000,
filed an application with FERC to transfer these compressor facilities to El
Paso Field Services. These asset transfers will not have a material adverse
effect on our financial position, results of operations, or cash flows.

     In March 2000, we received complaints from certain gas processors and
gatherers in the Permian Basin alleging that our cost allocations relating to
Waha gas compression facilities have resulted in passing non-jurisdictional
gathering costs to our jurisdictional customers. As a result of the complaints,
we executed an agreement with the complainants in June 2000 that provides for
the abandonment and conveyance to El Paso Field Services of certain compression
facilities at Waha with corresponding fuel adjustments. In August 2000, we filed
an application with FERC to transfer these assets to El Paso Field Services. The
impact of this agreement will not materially impact our financial position,
results of operations, or cash flows.

     Several of our customers have filed complaints requesting that FERC order
us to cease and desist from selling primary firm delivery point capacity at the
Southern California Gas Company Topock delivery point in excess of the
downstream capacity available at that point and to cease and desist from
overselling firm mainline capacity on the east-end of our mainline system.
Various technical conferences have been held regarding these matters. In May
2000, the parties agreed to use FERC's alternative dispute resolution services
to resolve these matters. A series of alternative dispute resolution meetings
were held during the summer of 2000 but have failed to produce a settlement. In
October 2000, FERC ordered us to make a one time allocation of available
delivery point capacity at the Southern California Gas Company Topock delivery
point among affected firm shippers, but deferred action on east-end and
systemwide capacity allocation issues. We are preparing to implement the
required delivery point capacity allocation.

     In January 2000, Northwest Pipeline Corporation filed a complaint alleging
that our scheduling procedures applicable to the Ignacio, Colorado interconnect
are inconsistent with applicable general industry standards and have resulted in
excessive imbalances on Northwest's system. In March 2000, FERC granted the
complaint and required imbalances incurred by Northwest as a result of our
scheduling practices to be transferred to our system. The result will not
materially impact our financial position, results of operations or cash flows.

     In April 2000, the California Public Utilities Commission (CPUC) filed a
complaint alleging that our sale of capacity to El Paso Merchant Energy Company,
an affiliated company, was anticompetitive and an abuse of the affiliate
relationship under FERC's policies. The CPUC served data requests to us and El
Paso Merchant Energy, which have been either substantially answered or, in the
case of El Paso Merchant Energy, contested. In August 2000, the CPUC filed a
motion requesting that our contract with El Paso Merchant Energy be abrogated
and Southern California Edison Company requested that the original complaint be
set for hearings. The matter is pending at FERC.

     As an interstate pipeline system, we are subject to FERC audits of our
books and records. We currently have an open audit covering the years 1990
through 1995. Also, from time to time, the FERC audit staff requests supporting
documentation from us as evidence of our compliance.

     As changes in the regulatory and economic environment evolve and our
pipelines continue to experience discounting of rates and unsubscribed capacity,
we will continue to evaluate the application of regulatory accounting
principles. Factors which could impact this assessment include an inability to
recover cost increases under rate caps and rate case moratoriums, an inability
to recover capitalized costs, including an adequate return on those costs
through the ratemaking process, excess capacity or significant discounting of
rates in the markets we serve, and the impacts of ongoing initiatives in, and
deregulation of, the natural gas industry.

                                        6
<PAGE>   8

     As our rate and regulatory matters are fully and unconditionally resolved,
we may either recognize additional refund obligations, non-cash write-downs of
previously established assets, or non-cash benefits to finalize previously
estimated liabilities. While we cannot predict with certainty the final outcome
or timing of the final resolution of our rates and regulatory matters, the
outcome of our current re-contracting and capacity subscription efforts, or the
outcome of ongoing industry trends and initiatives, we believe the ultimate
resolution of these issues will not have a material adverse effect on our
financial position, results of operations, or cash flows.

  Legal Proceedings

     In November 1993, TransAmerican Natural Gas Corporation filed a complaint
in a Texas state court against us which sought approximately $7.5 billion in
actual and punitive damages related to our 1990 settlement agreement with
TransAmerican and others. TransAmerican's complaint advanced ten causes of
action. Some of the causes of action were previously dismissed. Trial on the
remaining claims began on
May 1, 2000. During the trial commencement, all claims against all defendants
were settled. The settlement had no material adverse effect on our financial
position, results of operations, or cash flows.

     In April 1996, a former employee of TransAmerican filed a related case in
Harris County, Texas, Vickroy E. Stone v. Godwin & Carlton, P.C., et al.,
seeking other damages in unspecified amounts related to litigation consulting
work allegedly performed for various entities, including us, in cases involving
TransAmerican. In June 1998, the court granted our motion for summary judgment
and dismissed all claims in the Stone litigation. In May 2000, the Texas Court
of Appeals in Houston, Texas, upheld the trial court's rulings, except for one
claim relating to failure to pay Stone a bonus and, in September 2000, the Court
of Appeals denied motions for rehearing. We have filed a petition for review
with the Texas Supreme Court. Based on information available at this time, we
believe that the claims asserted against us in this case have no factual or
legal basis.

     We are a named 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. We have also been named
defendants in a similar class action suit, Quinque Operating Company v. Gas
Pipelines. This complaint alleges that the defendants mismeasured natural gas
volumes and heating content of natural gas on non-federal and non-Native
American lands. The Quinque complaint was transferred to the same court handling
the Grynberg complaint. We believe both complaints are without merit.

     On August 19, 2000, a mainline transmission line, which we own and operate,
ruptured at the crossing of the Pecos River near Carlsbad, New Mexico resulting
in the deaths of twelve individuals. In September 2000, we were served with a
complaint for damages in Heady, et al. v. EPEC and EPNG, filed in state district
court in Harris County, Texas, brought on behalf of four persons. In October
2000, we were served with a complaint for damages in Smith v. EPEC and EPNG,
filed in federal district court in Albuquerque, New Mexico, brought on behalf of
another person. Both complaints are for damages for personal injuries and
wrongful death. Our response in each case is due November 24, 2000. Also, in
October 2000, Smith v. EPNG and EPEC was filed against us in state district
court in Harris County, Texas for damages. To date, the plaintiff has not served
us with this complaint. The National Transportation Safety Board is conducting
an investigation into the cause of the rupture.

     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 to have a
material adverse effect on our financial position, results of operations, 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

                                        7
<PAGE>   9

environment of the disposal or release of specified substances at current and
former operating sites. As of September 30, 2000, we had reserved $20 million
for expected environmental costs.

     In addition, we expect to make capital expenditures of approximately $17
million for the years 2001 through 2007 for environmental matters primarily
relating to compliance with air regulations and control of water discharges.
Some of our subsidiaries have been designated, have received notice that they
could be designated, or have been asked for information to determine whether
they could be designated as a potentially responsible party with respect to 4
active sites under CERCLA.

     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.

6. NEW ACCOUNTING PRONOUNCEMENTS NOT YET ADOPTED

  Accounting for Derivative Instruments and Hedging Activities

     In June of 1998, the Financial Accounting Standards Board (FASB) issued
Statement of Financial Accounting Standards (SFAS) No. 133, Accounting for
Derivative Instruments and Hedging Activities. In June of 1999, the FASB
extended the adoption date of SFAS No. 133 through the issuance of SFAS No. 137,
Deferral of the Effective Date of SFAS 133. In June 2000, the FASB issued SFAS
No. 138, Accounting for Certain Derivative Instruments and Certain Hedging
Activities, which also amended SFAS No. 133. SFAS No. 133, and its amendments
and interpretations, establishes accounting and reporting standards for
derivative instruments, including derivative instruments embedded in other
contracts, and derivative instruments used for hedging activities. It will
require that we measure all derivative instruments at their fair value, and
classify them as either assets or liabilities on our balance sheet, with a
corresponding offset to income or other comprehensive income depending on their
designation, their intended use, or their ability to qualify as hedges under the
standard.

     We will adopt SFAS No. 133 beginning January 1, 2001, and do not believe it
will have a material impact on our financial position, results of operations, or
cash flows.

  Revenue Recognition in Financial Statements

     In December 1999, the Securities and Exchange Commission issued Staff
Accounting Bulletin (SAB) No. 101, Revenue Recognition in Financial Statements,
to provide guidance for revenue recognition issues and disclosure requirements.
SAB No. 101 offers guidelines, examples, and explanations for certain matters
relating to the recognition of revenue and will be effective for us in the
fourth quarter of 2000. We do not believe the adoption of SAB No. 101 will have
a material impact on our financial position, results of operations, or cash
flows.

  Accounting for Transfers and Servicing of Financial Assets and Extinguishments
of Liabilities

     In September 2000, the FASB issued SFAS No. 140, Accounting for Transfers
and Servicing of Financial Assets and Extinguishments of Liabilities, which
replaces SFAS No. 125. This statement revises the standards for accounting for
securitizations and other transfers of financial assets and collateral and
requires certain disclosures, but carries over most of SFAS No. 125's provisions
without reconsideration. This standard has various effective dates, the earliest
of which is for fiscal years ending after December 15, 2000. We are currently
evaluating the effects of this pronouncement.

                                        8
<PAGE>   10

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

     The information contained in this section updates, and should be read 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, 1999, in addition to
the financial statements and notes presented in Item 1 of this Quarterly Report
on Form 10-Q.

                             RESULTS OF OPERATIONS

<TABLE>
<CAPTION>
                                                     QUARTER           NINE MONTHS
                                                      ENDED               ENDED
                                                  SEPTEMBER 30,       SEPTEMBER 30,
                                                 ----------------    ----------------
                                                  2000      1999      2000      1999
                                                 ------    ------    ------    ------
                                                 (IN MILLIONS, EXCEPT VOLUME AMOUNTS)
<S>                                              <C>       <C>       <C>       <C>
Operating revenues.............................  $  121    $  120    $  356    $  359
Operating expenses.............................     (60)      (67)     (189)     (196)
Other income, net..............................       3         1         3         1
                                                 ------    ------    ------    ------
  EBIT.........................................  $   64    $   54    $  170    $  164
                                                 ======    ======    ======    ======
Throughput volumes (BBtu/d)(1).................   4,617     3,992     4,185     3,956
                                                 ======    ======    ======    ======
</TABLE>

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

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

  Third Quarter 2000 Compared to Third Quarter 1999

     Operating revenues for the quarter ended September 30, 2000, were $1
million higher than the same period in 1999 resulting from higher transportation
revenues in 2000.

     Operating expenses for the quarter ended September 30, 2000, were $7
million lower than the same period in 1999. Lower operating costs and lower
system fuel usage in the third quarter of 2000 and the resolution of a contested
rate matter with a customer in the third quarter of 1999 were partially offset
by revised estimates of regulatory recoveries and environmental liabilities in
the third quarter of 1999.

     Other income, net for the quarter ended September 30, 2000, was $2 million
higher than the same period 1999 due to the sale of non-pipeline assets in the
third quarter of 2000.

  Nine Months Ended 2000 Compared to Nine Months Ended 1999

     Operating revenues for the nine months ended September 30, 2000, were $3
million lower than the same period in 1999. Lower revenues from relinquished
capacity were partially offset by higher transportation revenues in the third
quarter of 2000.

     Operating expenses for the nine months ended September 30, 2000, were $7
million lower than the same period in 1999. Lower overall operating costs in
2000 and the resolution of a contested rate matter with a customer in the third
quarter of 1999 were partially offset by an unfavorable producer settlement and
an asset refunctionalization settlement in the second quarter of 2000 as well as
revised estimates of regulatory recoveries and environmental liabilities in the
third quarter of 1999.

     Other income, net for the nine months ended September 30, 2000, was $2
million higher than the same period in 1999 due to the sale of non-pipeline
assets in the third quarter of 2000.

                                        9
<PAGE>   11

NON-AFFILIATED INTEREST AND DEBT EXPENSE

     Non-affiliated interest and debt expense for the quarter and nine months
ended September 30, 2000, was $3 million and $8 million lower than the same
periods in 1999. The decreases were due to reduced average borrowings, primarily
long term debt and higher capitalized interest.

AFFILIATED INTEREST INCOME, NET

     Affiliated interest income, net for the nine months ended September 30,
2000, was $11 million higher than the same period in 1999 due to increased
average borrowing rates with El Paso Energy in 2000.

INCOME TAX EXPENSE

     The effective income tax rate for the quarters ended September 30, 2000 and
1999, was 38% for each period. The effective income tax rates for the nine
months ended September 30, 2000 and 1999, were 39% and 38%. The effective tax
rates were higher than the statutory rate of 35% due to state income taxes.

                                       10
<PAGE>   12

           CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

     We have made statements in this document that constitute forward-looking
statements, as that term is defined in the Private Securities Litigation Reform
Act of 1995. These statements are subject to risks and uncertainties.
Forward-looking statements include information concerning possible or assumed
future results of operations. These statements may relate to information or
assumptions about:

     - capital and other expenditures;

     - dividends;

     - financing plans;

     - capital structure;

     - cash flow;

     - pending legal proceedings and claims, including environmental matters;

     - future economic performance;

     - operating income;

     - cost savings;

     - management's plans; and

     - goals and objectives for future operations.

     Important factors that could cause actual results to differ materially from
estimates or projections contained in forward-looking statements include, among
others, the following:

     - the increasing competition within our industry;

     - the timing and extent of changes in commodity prices for natural gas and
       power;

     - the uncertainties associated with customer contract expirations on our
       pipeline systems;

     - the potential contingent liabilities and tax liabilities related to our
       acquisitions; and

     - the conditions of equity and other capital markets.

     These risk factors are more fully described in our other filings with the
Securities and Exchange Commission, including our Annual Report on Form 10-K for
the year ended December 31, 1999.

ITEM 3. QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK

     This information updates, and should be read in conjunction with,
information disclosed in Part II, Item 7A in our Annual Report on Form 10-K for
the year ended December 31, 1999, 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 market risks from those reported in our
Annual Report on Form 10-K for the year ended December 31, 1999.

                                       11
<PAGE>   13

                          PART II -- OTHER INFORMATION

ITEM 1. LEGAL PROCEEDINGS

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

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

     Each exhibit identified below is filed as a part of this report.

<TABLE>
<CAPTION>
      EXHIBIT
      NUMBER
      -------                               DESCRIPTION
<C>                 <S>
        10.A        -- $2,000,000,000 364-Day Revolving Credit and Competitive
                       Advance Facility Agreement dated August 4, 2000, by and
                       among El Paso Energy Corporation, El Paso Natural Gas
                       Company, Tennessee Gas Pipeline Company, the several
                       banks and other financial institutions from time to time
                       parties to the Agreement, The Chase Manhattan Bank,
                       Citibank N.A. and ABN Amro Bank, N.V. as co-documentation
                       agents for the Lenders and Bank of America, N.A. as
                       syndication agent for the Lenders.
        10.B        -- $1,000,000,000 3-Year Revolving Credit and Competitive
                       Advance Facility Agreement dated August 4, 2000, by and
                       among El Paso Energy Corporation, El Paso Natural Gas
                       Company, Tennessee Gas Pipeline Company, the several
                       banks and other financial institutions from time to time
                       parties to the Agreement, The Chase Manhattan Bank,
                       Citibank N.A. and ABN Amro Bank, N.V. as co-documentation
                       agents for the Lenders and Bank of America, N.A. as
                       syndication agent for the Lenders.
        27          -- Financial Data Schedule
</TABLE>

     Undertaking

          The undersigned hereby undertakes, 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 long-term debt of El Paso Natural Gas Company and its
     consolidated subsidiaries not filed herewith for the reason that the total
     amount of securities authorized under any of such instruments does not
     exceed 10 percent of the total consolidated assets of El Paso Natural Gas
     Company and its consolidated subsidiaries.

     b. Reports on Form 8-K

        None.

                                       12
<PAGE>   14

                                   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.

                                           EL PASO NATURAL GAS COMPANY

Date: November 9, 2000                             /s/ H. BRENT AUSTIN
                                            ------------------------------------
                                                      H. Brent Austin
                                                Executive Vice President and
                                                  Chief Financial Officer

Date: November 9, 2000                            /s/ JEFFREY I. BEASON
                                            ------------------------------------
                                                     Jeffrey I. Beason
                                            Senior Vice President and Controller
                                                 (Chief Accounting Officer)

                                       13
<PAGE>   15

                               INDEX TO EXHIBITS

<TABLE>
<CAPTION>
      EXHIBIT
      NUMBER
      -------                               DESCRIPTION
<C>                 <S>
        10.A        -- $2,000,000,000 364-Day Revolving Credit and Competitive
                       Advance Facility Agreement dated August 4, 2000, by and
                       among El Paso Energy Corporation, El Paso Natural Gas
                       Company, Tennessee Gas Pipeline Company, the several
                       banks and other financial institutions from time to time
                       parties to the Agreement, The Chase Manhattan Bank,
                       Citibank N.A. and ABN Amro Bank, N.V. as co-documentation
                       agents for the Lenders and Bank of America, N.A. as
                       syndication agent for the Lenders.
        10.B        -- $1,000,000,000 3-Year Revolving Credit and Competitive
                       Advance Facility Agreement dated August 4, 2000, by and
                       among El Paso Energy Corporation, El Paso Natural Gas
                       Company, Tennessee Gas Pipeline Company, the several
                       banks and other financial institutions from time to time
                       parties to the Agreement, The Chase Manhattan Bank,
                       Citibank N.A. and ABN Amro Bank, N.V. as co-documentation
                       agents for the Lenders and Bank of America, N.A. as
                       syndication agent for the Lenders.
        27          -- Financial Data Schedule
</TABLE>