<PAGE>
 
                                 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, 1998
                                      OR
[_]          TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d)
                    OF  THE SECURITIES EXCHANGE ACT OF 1934
         For the transition period _______________ to ________________
 
                          COMMISSION FILE NO. 0-25842

                 PG&E GAS TRANSMISSION, NORTHWEST CORPORATION
            (Exact name of registrant as specified in its charter)

           CALIFORNIA                                   94-1512922
   (State or other jurisdiction of        (I.R.S. employer Identification No.)
   incorporation or organization)
2100 SW RIVER PARKWAY, PORTLAND, OR                         97201
(Address of principal executive offices)                  (Zip code)


      REGISTRANT'S TELEPHONE NUMBER, INCLUDING AREA CODE:  (503) 833-4000
                                        

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 twelve 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 November 13, 1998.

1,000 shares of common stock no par value.  (All shares are owned by PG&E Gas
Transmission Corporation.)

REGISTRANT MEETS THE CONDITIONS SET FORTH IN GENERAL INSTRUCTION (H) (1) (a) AND
    (b) OF FORM 10-Q AND IS THEREFORE FILING THIS FORM 10-Q WITH THE REDUCED
                               DISCLOSURE FORMAT.
<PAGE>
 
TABLE OF CONTENTS
-----------------
<TABLE>
<CAPTION>

PART I.  FINANCIAL INFORMATION                                                 Page
------------------------------                                

Item 1.    Consolidated Financial Statements
<S>              <C>                                                           <C>                
                 Statements of Consolidated Income                              1                 
                                                                                                  
                 Consolidated Balance Sheets                                    2                 
                                                                                                  
                 Statements of Consolidated Common Stock Equity                 4                 
                                                                                                  
                 Statements of Consolidated Cash Flows                          5                 
                                                                                                  
                 Notes to Consolidated Financial Statements                     6                 
                                                                                                  
                          Note 1.  Basis of Presentation                        6                 
                                                                                                  
                          Note 2.  Contingencies                                7                 
                                                                                                  
                          Note 3.  Other Comprehensive Income                   7                 
                                                                                                  
Item 2.          Management's Discussion and Analysis of Financial Condition                      
                 and Results of Operations                                      8                 
 
PART II.  OTHER INFORMATION
------------------------------
 
Item 6.          Exhibits and Reports on Form 8-K                               17

Signatures                                                                      18
</TABLE>
<PAGE>
 
PART I: FINANCIAL INFORMATION
-----------------------------

ITEM 1.  CONSOLIDATED FINANCIAL STATEMENTS
         ---------------------------------
<TABLE>
<CAPTION>
------------------------------------------------------------------------------------------------------------------------------------

                                                     STATEMENTS OF CONSOLIDATED INCOME
                                                                (UNAUDITED)
------------------------------------------------------------------------------------------------------------------------------------

                                                                  THREE MONTHS ENDED                    NINE MONTHS ENDED
                                                                     SEPTEMBER 30,                        SEPTEMBER 30,
(IN THOUSANDS)                                                  1998              1997               1998               1997
------------------------------------------------------------------------------------------------------------------------------------

<S>                                                        <C>             <C>               <C>                  <C>    
 
OPERATING REVENUES:                                                                                                            
Gas transportation                                         $    45,471      $    48,971      $     138,048        $     142,640 
Gas transportation for affiliates                               12,712           12,143             37,924               36,744 
Other                                                              220              232                539                  492 
-----------------------------------------------------------------------------------------------------------------------------------
     TOTAL OPERATING REVENUES                                   58,403           61,346            176,511              179,876 
-----------------------------------------------------------------------------------------------------------------------------------
OPERATING EXPENSES:
Administrative and general                                       8,621            8,859             22,679               26,915  
Operations and maintenance                                       3,881            5,102             11,527               13,418  
Depreciation and amortization                                    9,741           10,330             29,355               30,937  
Property and other taxes                                         2,825            2,826              8,759                8,621  
-----------------------------------------------------------------------------------------------------------------------------------

     TOTAL OPERATING EXPENSES                                   25,068           27,117             72,320               79,891  
-----------------------------------------------------------------------------------------------------------------------------------

OPERATING INCOME                                                33,335           34,229            104,191               99,985  
-----------------------------------------------------------------------------------------------------------------------------------
                                                                                                                                 
OTHER INCOME AND (INCOME DEDUCTIONS):                                                                                            
Investment development                                               -           (4,174)                 -              (11,270) 
Allowance for equity funds used during construction                417               96                730                  329  
Interest income                                                     43              160                180                  580  
Other -  net                                                     1,065             (117)               866               (1,156) 
-----------------------------------------------------------------------------------------------------------------------------------
     TOTAL OTHER INCOME AND (INCOME DEDUCTIONS)                  1,525           (4,035)             1,776              (11,517) 
----------------------------------------------------------------------------------------------------------------------------------- 

                                                                                                                                 
INTEREST EXPENSE:                                                                                                                
Interest on long-term debt                                      10,704           11,711             31,907               35,405  
Allowance for borrowed funds used during construction             (432)             (69)              (753)                (223) 
Other interest charges                                             346              296              1,079                  835  
-----------------------------------------------------------------------------------------------------------------------------------
     NET INTEREST EXPENSE                                       10,618           11,938             32,233               36,017  
----------------------------------------------------------------------------------------------------------------------------------- 

INCOME FROM CONTINUING OPERATIONS                                                                                                
     BEFORE INCOME TAXES                                        24,242           18,256             73,734               52,451  
                                                                                                                                 
INCOME TAX EXPENSE                                               8,511            7,008             27,805               20,560  
-----------------------------------------------------------------------------------------------------------------------------------
INCOME FROM CONTINUING OPERATIONS                               15,731           11,248             45,929               31,891  
----------------------------------------------------------------------------------------------------------------------------------- 

INCOME (LOSS) FROM DISCONTINUED OPERATIONS                                                                                       
     BEFORE INCOME TAXES                                             -                -                  -              (11,901) 
INCOME TAX (EXPENSE) BENEFIT                                         -                -                  -                4,157 
-----------------------------------------------------------------------------------------------------------------------------------
NET INCOME                                                      15,731           11,248             45,929               24,147  
-----------------------------------------------------------------------------------------------------------------------------------
OTHER COMPREHENSIVE INCOME, NET OF TAX:                                                                                          
                                                                                                                                 
FOREIGN CURRENCY TRANSLATION ADJUSTMENT                              -            5,478                  -                 (292) 
-----------------------------------------------------------------------------------------------------------------------------------
COMPREHENSIVE INCOME                                       $    15,731      $    16,726      $      45,929        $      23,855
------------------------------------------------------------------------------------------------------------------------------------

</TABLE>

         The accompanying Notes to Consolidated Financial Statements 
                   are an integral part of these statements.

                                       1
<PAGE>
 
<TABLE>
<CAPTION>
 --------------------------------------------------------------------------------------------------------------------------
                                                 CONSOLIDATED BALANCE SHEETS
                                                         (UNAUDITED)
---------------------------------------------------------------------------------------------------------------------------
                                                           ASSETS
---------------------------------------------------------------------------------------------------------------------------
                                                                                       SEPTEMBER 30,           DECEMBER 31, 
(IN THOUSANDS)                                                                             1998                    1997  
---------------------------------------------------------------------------------------------------------------------------
<S>                                                                                    <C>                     <C>  
 
PROPERTY, PLANT, AND EQUIPMENT:
Property, plant and equipment in service                                               $ 1,495,496              $ 1,478,735
Accumulated depreciation                                                                  (474,518)                (444,408)
---------------------------------------------------------------------------------------------------------------------------
  Net plant in service                                                                   1,020,978                1,034,327
Construction work in progress                                                               31,294                   13,870
---------------------------------------------------------------------------------------------------------------------------
     TOTAL PROPERTY, PLANT & EQUIPMENT - NET                                             1,052,272                1,048,197
---------------------------------------------------------------------------------------------------------------------------
 
CURRENT ASSETS:
Cash and cash equivalents                                                                    2,814                   48,249
Accounts receivable - gas transportation                                                    15,211                   16,701
Accounts receivable - affiliated companies                                                   4,698                    4,964
Accounts receivable - other                                                                  9,586                    6,747
Inventories (at average cost)                                                                6,766                    6,523
Prepayments and other current assets                                                           283                    4,282
---------------------------------------------------------------------------------------------------------------------------
     TOTAL CURRENT ASSETS                                                                   39,358                   87,466
---------------------------------------------------------------------------------------------------------------------------
 
DEFERRED CHARGES:
Income tax related                                                                          25,422                   25,482
Deferred charge on reacquired debt                                                          12,750                   13,654
Unamortized debt expense                                                                     3,722                    4,014
Regulatory assets                                                                            6,287                    6,430
Other                                                                                          183                      240
---------------------------------------------------------------------------------------------------------------------------
     TOTAL DEFERRED CHARGES                                                                 48,364                   49,820
---------------------------------------------------------------------------------------------------------------------------
 
TOTAL ASSETS                                                                           $ 1,139,994              $ 1,185,483
---------------------------------------------------------------------------------------------------------------------------
</TABLE>

         The accompanying Notes to Consolidated Financial Statements 
                   are an integral part of these statements.

                                       2
<PAGE>
 
<TABLE>
<CAPTION>
------------------------------------------------------------------------------------------------------------------------- 
                                               CONSOLIDATED BALANCE SHEETS
                                                       (UNAUDITED)
-------------------------------------------------------------------------------------------------------------------------
                                              CAPITALIZATION AND LIABILITIES
                                                                                    SEPTEMBER 30,            DECEMBER 31, 
(IN THOUSANDS)                                                                          1998                     1997
-------------------------------------------------------------------------------------------------------------------------
<S>                                                                                 <C>                      <C> 
CAPITALIZATION:
Common stock - no par value, 1,000 shares authorized,
     issued and outstanding                                                         $      85,474            $     85,474
Additional paid-in capital                                                                192,717                 192,717
Reinvested earnings                                                                        69,465                 153,536
-------------------------------------------------------------------------------------------------------------------------
     Total common stock equity                                                            347,656                 431,727
Long-term debt                                                                            587,604                 563,499
-------------------------------------------------------------------------------------------------------------------------
     TOTAL CAPITALIZATION                                                                 935,260                 995,226
-------------------------------------------------------------------------------------------------------------------------
 
CURRENT LIABILITIES:
Long-term debt -  current portion                                                             447                     419
Accounts payable and other accrued liabilities                                             31,782                  31,208
Accrued taxes                                                                               3,347                     813
-------------------------------------------------------------------------------------------------------------------------
     TOTAL CURRENT LIABILITIES                                                             35,576                  32,440
-------------------------------------------------------------------------------------------------------------------------
 
DEFERRED CREDITS:
Deferred income taxes                                                                     157,945                 145,727
Other                                                                                      11,213                  12,090
-------------------------------------------------------------------------------------------------------------------------
     TOTAL DEFERRED CREDITS                                                               169,158                 157,817
-------------------------------------------------------------------------------------------------------------------------
 
CONTINGENCIES (SEE NOTE 2)                                                                      -                       -
------------------------------------------------------------------------------------------------------------------------- 
 
TOTAL CAPITALIZATION AND LIABILITIES                                             $      1,139,994       $       1,185,483
-------------------------------------------------------------------------------------------------------------------------
</TABLE>

         The accompanying Notes to Consolidated Financial Statements 
                   are an integral part of these statements.

                                       3
<PAGE>
 
<TABLE>
<CAPTION>
------------------------------------------------------------------------------------------------------------------- 
                                   STATEMENTS OF CONSOLIDATED COMMON STOCK EQUITY
                                                    (UNAUDITED)
 ------------------------------------------------------------------------------------------------------------------
                                                                                               NINE MONTHS ENDED
                                                                                                 SEPTEMBER 30,
(IN THOUSANDS)                                                                                1998            1997
-------------------------------------------------------------------------------------------------------------------
 
<S>                                                                                     <C>            <C> 
BALANCE AT BEGINNING OF PERIOD                                                           $   431,727    $   510,502
     Comprehensive income
            Net income                                                                        45,929         24,147
            Other comprehensive income                                                             
                 Foreign currency translation adjustment                                           -           (292)
     Return of Capital of PG&E Energy Trading to parent company                                    -        (49,275)
     Dividend paid to parent company                                                        (130,000)       (52,000)
-------------------------------------------------------------------------------------------------------------------
BALANCE AT END OF PERIOD                                                                 $   347,656    $   433,082
-------------------------------------------------------------------------------------------------------------------
</TABLE>

         The accompanying Notes to Consolidated Financial Statements 
                   are an integral part of these statements.

                                       4
<PAGE>
 
<TABLE>
<CAPTION>
----------------------------------------------------------------------------------------------------------------------------- 
                                            STATEMENTS OF CONSOLIDATED CASH FLOWS
                                                         (UNAUDITED)
-----------------------------------------------------------------------------------------------------------------------------
                                                                                                  NINE MONTHS ENDED
                                                                                                     SEPTEMBER 30,
-----------------------------------------------------------------------------------------------------------------------------
(IN THOUSANDS)                                                                                 1998                  1997
-----------------------------------------------------------------------------------------------------------------------------
<S>                                                                                     <C>                 <C>    
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income                                                                              $        45,929     $        24,147    
Adjustments to reconcile net income to net cash provided by                                                                    
  operating activities:                                                                                                        
        Depreciation and amortization                                                            31,662              32,886    
        Discontinued operations                                                                       -               7,744    
        Deferred income taxes                                                                    12,278              11,439    
        Allowance for equity funds used during construction                                        (730)               (329)   
Changes in operating assets and liabilities:                                                                                   
        Accounts receivable - gas transportation                                                  1,490               4,815    
        Accounts receivable - affiliated companies                                                  266              14,654    
        Accounts receivable - other                                                              (2,840)              2,294    
        Accounts payable and other accrued liabilities                                              574              (1,195)   
        Accrued taxes                                                                             2,534               1,571    
        Other working capital                                                                     3,756               2,949    
Other - net                                                                                        (677)               (731)   
---------------------------------------------------------------------------------------------------------------------------
          NET CASH PROVIDED BY OPERATING ACTIVITIES                                              94,242             100,244    
---------------------------------------------------------------------------------------------------------------------------    
                                                                                                                               
CASH FLOWS FROM INVESTING ACTIVITIES:                                                                                          
Sale of subsidiaries to affiliated company                                                            -              42,000    
Investment expenditures                                                                               -              (2,891)   
Sale of fixed assets                                                                                  -               5,303    
Construction expenditures                                                                       (32,870)            (27,737)   
Allowance for borrowed funds used during construction                                              (753)               (223)   
---------------------------------------------------------------------------------------------------------------------------
          NET CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES                                   (33,623)             16,452    
---------------------------------------------------------------------------------------------------------------------------    
                                                                                                                               
CASH FLOWS FROM FINANCING ACTIVITIES:                                                                                          
Repayment of long-term debt                                                                     (64,140)            (66,168)   
Long-term debt issued, net of issuance costs                                                     88,086                   -    
Dividend paid to parent                                                                        (130,000)            (52,000)   
---------------------------------------------------------------------------------------------------------------------------
          NET CASH USED IN FINANCING ACTIVITIES                                                (106,054)           (118,168)   
---------------------------------------------------------------------------------------------------------------------------    
                                                                                                                               
NET CHANGE IN CASH AND CASH EQUIVALENTS                                                         (45,435)             (1,472)   
                                                                                                                               
CASH AND CASH EQUIVALENTS AT JANUARY 1                                                           48,249              11,969    
---------------------------------------------------------------------------------------------------------------------------    
CASH AND CASH EQUIVALENTS AT SEPTEMBER 30                                                $        2,814     $        10,497    
---------------------------------------------------------------------------------------------------------------------------    
                                                                                                                               
SUPPLEMENTAL DISCLOSURES OF CASH FLOW                                                                                          
   INFORMATION:                                                                                                                
Cash paid for (received from):                                                                                                 
          Interest                                                                       $       24,578     $        28,654    
          Income taxes                                                                   $       17,513     $        (3,451)   
---------------------------------------------------------------------------------------------------------------------------    
</TABLE>

         The accompanying Notes to Consolidated Financial Statements 
                   are an integral part of these statements.

                                       5
<PAGE>
 
NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (UNAUDITED)
-------------------------------------------------------------------------------


NOTE 1:  BASIS OF PRESENTATION
------------------------------

  Effective January 1, 1998, Pacific Gas Transmission Company, incorporated in
California in 1957, changed its name to PG&E Gas Transmission, Northwest
Corporation (PG&E GT-NW).   PG&E GT-NW is affiliated with, but is not the same
company as, Pacific Gas and Electric Company, the gas and electric company
serving Northern and Central California.  PG&E Corporation is the ultimate
corporate parent for both PG&E GT-NW and Pacific Gas and Electric Company.

  The accompanying unaudited consolidated financial statements, which have been
prepared in accordance with interim period reporting requirements, reflect the
results for PG&E GT-NW and its wholly owned subsidiaries, including Pacific Gas
Transmission International, Inc. (PGT International) and the following
subsidiaries through their respective dates of disposition:

  Through June 30, 1997:

          PG&E Energy Trading Corporation (PG&E Energy Trading)

  Through September 26, 1997:

          PG&E Gas Transmission Australia Pty Ltd (PG&E Australia)
 
          PG&E Gas Transmission Queensland Pty Limited (PG&E Queensland)

  On June 30, 1997, PG&E GT-NW distributed all of the shares of PG&E Energy
Trading to PG&E GT-NW's sole shareholder, PG&E Gas Transmission Corporation.
PG&E Gas Transmission Corporation immediately thereafter distributed these
shares to its sole shareholder, PG&E Corporation.  Accordingly, PG&E Energy
Trading's results are reported as discontinued operations.

  On September 26, 1997, PG&E GT-NW sold all of its investments in Australia to
another PG&E Corporation affiliate.  The subsidiaries sold included PG&E
Queensland, the operator of the PG&E Queensland Gas Pipeline, and PG&E
Australia.  The Company also sold its investment in the PG&E Qld Trust.  The
PG&E Qld Trust, which held the assets of the PG&E Queensland Gas Pipeline, was
beneficially owned by PGT International (a PG&E GT-NW wholly owned subsidiary).

  PG&E GT-NW and its subsidiaries are collectively referred to herein as the
"Company."  This information should be read in conjunction with the Consolidated
Financial Statements and Notes to Consolidated Financial Statements included in
Item 8, Financial Statements and Supplementary Data, in the Company's Form 10-K
for the fiscal year ended December 31, 1997.

  In the opinion of management, the accompanying statements reflect all
adjustments necessary to present a fair statement of the financial position and
results of operations for the interim periods.  All material adjustments are of
a normal recurring nature unless otherwise disclosed in this Form 10-Q.
Subsidiary intercompany accounts and transactions have been eliminated.  Prior
year's amounts in the consolidated financial statements have been reclassified
where necessary to conform to the 1998 presentation.  Results of operations for
interim periods are not necessarily indicative of results to be expected for a
full year.

                                       6
<PAGE>
 
NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (UNAUDITED)
-------------------------------------------------------------------------------
 

NOTE 2:  CONTINGENCIES
----------------------

  1994 RATE CASE - In September 1996, the Federal Energy Regulatory Commission
(FERC) approved, without modification, the proposed settlement of PG&E GT-NW's
rate case.  The rate case was initially filed on February 28, 1994, while the
proposed settlement was filed with the FERC on March 21, 1996.  In March and
June 1998, the FERC denied requests by several shippers for rehearing and
reaffirmed its approval of the settlement.  In May 1998, three shippers
petitioned for judicial review of the FERC Orders by the United States Court of
Appeals for the District of Columbia.  In the event the settlement were to be
modified as a result of an appeal, PG&E GT-NW would be required to implement the
results as ordered by the court but would also have the right to appeal any
order that modifies the settlement.


NOTE 3:  OTHER COMPREHENSIVE INCOME
-----------------------------------

  For the nine months ended September 30, 1997, PG&E GT-NW's other comprehensive
loss was $0.3 million, reflecting the transfer of the foreign currency
translation adjustments for the operations of the PG&E Queensland Gas Pipeline
and PG&E Energy Trading to an affiliate and PG&E Corporation, respectively.  As
stated in Note 1, the PG&E Queensland Gas Pipeline and PG&E Australia were sold
to another PG&E Corporation affiliate on September 26, 1997, and the shares of
PG&E Energy Trading were transferred to PG&E Corporation on June 30, 1997.


<TABLE>
<CAPTION>
<S>                                                 <C>                        <C>                       <C>  
                                                                                          TAX
NINE MONTHS ENDED SEPTEMBER 30, 1997                    BEFORE-TAX                     (EXPENSE)                    NET-OF-TAX
           (IN MILLIONS)                                  AMOUNT                       OR BENEFIT                     AMOUNT
-------------------------------------------      ----------------------        -----------------------      -----------------------
 
Foreign currency translation adjustments            $            (0.3)             $             0.0           $            (0.3)
                                                 ======================        =======================      =======================
</TABLE>



<TABLE>
<CAPTION>
                                                                                                                     ACCUMULATED
                                                                                         FOREIGN                        OTHER
   NINE MONTHS ENDED SEPTEMBER 30, 1997                                                 CURRENCY                    COMPREHENSIVE
               (IN MILLIONS)                                                              ITEMS                         INCOME
-------------------------------------------                                    -----------------------       -----------------------

<S>                                                                               <C>                          <C>  
Beginning Balance                                                                 $       (0.2)                 $        (0.2)
Current-period change                                                                     (0.3)                          (0.3)
                                                                               -----------------------       -----------------------

Ending Balance                                                                    $       (0.5)                 $        (0.5)
                                                                               =======================       =======================

</TABLE>

                                       7
<PAGE>
 
ITEM 2.   MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND
          ---------------------------------------------------------------
RESULTS OF OPERATIONS
---------------------


GENERAL
-------

  The unaudited consolidated financial statements include PG&E Gas Transmission,
Northwest Corporation (PG&E GT-NW) and its wholly owned subsidiary, Pacific Gas
Transmission International, Inc. (PGT International), and the following
subsidiaries through their respective dates of disposition:

  Through June 30, 1997:

          PG&E Energy Trading Corporation (PG&E Energy Trading)

  Through September 26, 1997:

          PG&E Gas Transmission Australia Pty Limited (PG&E Australia)

          PG&E Gas Transmission Queensland Pty Limited (PG&E Queensland)

  PG&E GT-NW and its subsidiaries are collectively referred to herein as the
"Company."  This information should be read in conjunction with the Consolidated
Financial Statements and Notes to Consolidated Financial Statements included in
Item 8, Financial Statements and Supplementary Data in the Company's Form 10-K
for the fiscal year ended December 31, 1997.

  The following discussion includes forward-looking statements that involve a
number of risks, uncertainties, and assumptions.  When used in Management's
Discussion and Analysis of Financial Condition and Results of Operations, words
such as "estimates," "expects," "intends," "anticipates," "plans," and similar
expressions identify those statements which are forward-looking.  Actual results
may differ materially from those expressed in the forward-looking statements.
The important factors that could cause actual results to differ materially from
those expressed in the forward-looking statements include, but are not limited
to, the ongoing restructuring of the gas industry, changes in future rate-
making, and the ability of the Company to expand its core pipeline business.

  PG&E GT-NW's transportation system provides access to natural gas from
producing fields in western Canada and extends from the British Columbia-Idaho
border to the Oregon-California border.  PG&E GT-NW's transportation system also
provides service to various delivery points in Idaho, Washington, and Oregon.
PG&E GT-NW's natural gas transportation services are regulated by the Federal
Energy Regulatory Commission (FERC or the Commission). Various safety issues are
subject to the jurisdiction of the United States Department of Transportation.

                                       8
<PAGE>
 
CHANGING REGULATORY ENVIRONMENT
-------------------------------

  During 1997 and 1998, the FERC issued several orders to standardize
communications and practices of pipelines.  In April 1998, the FERC issued Order
587-G which sets standards for electronic communication, nomination, and
imbalance procedures.  In May 1998, many companies, including PG&E GT-NW, filed
for rehearing of certain aspects of Order 587-G.  The order proposes, among
other items, that all business transactions be conducted on the public Internet.
Pipeline companies need to develop connections using internet tools, directory
services, and communication protocols to provide non-discriminatory access to
all electronic information.  In September 1998, the Commission issued an order
on rehearing clarifying certain aspects of Order 587-G and deferring the date
for processing transactions over the Internet from June 1999 to June 2000.

  In July 1998, the Commission issued Order 587-H which establishes new
nomination and scheduling procedures to offer shippers additional opportunities
to modify their nominations for service within a given day.  Such revised
procedures were implemented by PG&E GT-NW effective November 2, 1998.

  Also in July 1998, the FERC issued a Notice of Proposed Rulemaking (NOPR) that
addresses several short-term service issues.  The purpose of the NOPR is to
maximize competition in the marketplace, monitor transactions through increased
reporting, and mitigate market power where it exists.  The NOPR includes, among
other items, the removal of the price cap for the short-term market,
establishment of auctions for short-term capacity, permission for negotiated
terms and conditions with protections for recourse shippers, and removal of the
five-year matching cap in the right-of-first-refusal procedure.  Comments on the
NOPR are due in January 1999, and a final rulemaking is expected in mid 1999.

  Although the Company is planning some capital expenditures to adopt these
initiatives, they are not expected to have a material impact on PG&E GT-NW's
financial position, liquidity, or results of operations in the foreseeable
future.


FUTURE EXPANSIONS AND BUSINESS DEVELOPMENT
------------------------------------------

  In August 1998, the FERC granted PG&E GT-NW's application to expand its
pipeline capacity by upgrading three compressors on the northern portion of its
mainline system.  Approximately 72 percent of the additional new capacity of
56,000 decatherms per day (Dt/day) for annual service plus 20,000 Dt/day for
winter service has been contracted with customers for terms ranging from three
to seven years for the annual service and 15 years for the winter service. The
estimated cost of the project is $6.0 million, and the service was effective on
November 1, 1998.

  PG&E GT-NW intends to solicit expressions of interest for additional capacity
and will consider developing additional firm transportation service capacity to
its mainline system in the future if sufficient demand develops.  In addition to
mainline expansions and extensions off of its mainline system, PG&E GT-NW is
considering opportunities to expand its core pipeline business primarily within
its service territory.  Growth prospects are primarily focused on investing in
pipelines, storage, and gathering and processing capabilities.

                                       9
<PAGE>
 
ACCOUNTING FOR THE EFFECTS OF REGULATION
----------------------------------------

  PG&E GT-NW currently accounts for the economic effects of regulation in
accordance with the provisions of Statement of Financial Accounting Standards
(SFAS) No. 71, "Accounting for the Effects of Certain Types of Regulation."  As
a result of applying the provisions of SFAS No. 71, PG&E GT-NW has accumulated
approximately $59.5 million of regulatory assets as of September 30, 1998,
including $8.6 million for relocation costs associated with the transfer of its
headquarters from San Francisco, California to Portland, Oregon, and $2.5
million for pension benefits related to PG&E GT-NW's 1997 Workforce Management
Program (WMP).  Although PG&E GT-NW recorded a reserve against the deferred WMP
pension costs in 1997 and the relocation costs in 1996, management intends to
seek recovery of these costs as well as all other regulatory assets through
rates charged to customers.

                                       10
<PAGE>
 
RESULTS OF OPERATIONS
---------------------

  Selected operating results and other data are as follows:
 
<TABLE>
<CAPTION>
                                                                  Three Months Ended                  Nine Months Ended
                                                                    September 30,                       September 30,
                                                               1998                1997            1998              1997
                                                                     (In Millions)                      (In Millions)
<S>                                                      <C>                <C>              <C>              <C>   
Operating revenues                                        $       58.4       $       61.3     $     176.5      $      179.9
Operating expenses                                                25.1               27.1            72.3              79.9
                                                          ------------       ------------     -----------      ------------
   Operating income                                               33.3               34.2           104.2             100.0
Other income and (income deductions)                               1.5               (4.1)            1.7             (11.6)
Net interest expense                                              10.6               11.9            32.2              36.0
                                                          ------------       ------------     -----------      ------------
   Income from continuing operations before taxes                 24.2               18.2            73.7              52.4
Income tax expense                                                 8.5                7.0            27.8              20.6
                                                          ------------       ------------     -----------      ------------
   Income from continuing operations                              15.7               11.2            45.9              31.8
Income (loss) from discontinued operations                           -                  -               -              (7.7)
                                                          ------------       ------------     -----------      ------------
   Net income                                             $       15.7       $       11.2     $      45.9      $       24.1
                                                          ============       ============     ===========      ============
</TABLE>


  NET INCOME - Income from continuing operations for the three and nine month
periods ended September 30, 1998, increased $4.5 million and $14.1 million,
respectively, compared to the same periods in 1997.  The increases in the 1998
periods were primarily the result of lower operating expenses, lower investment
development expenses, and lower interest expense.

  OPERATING REVENUES - Operating revenues for the three and nine month periods
ended September 30, 1998, decreased $2.9 million and $3.4 million, respectively,
compared to the same periods in 1997.  The decreases in the 1998 periods were
due to the absence of revenue from the PG&E Queensland Gas Pipeline in 1998.
The PG&E Queensland Gas Pipeline, which was sold on September 26, 1997, realized
$2.9 million and $8.4 million of revenue for the three and nine month periods
ended September 30, 1997, respectively.  The decrease in revenue for the nine
month period ended September 30, 1998 was partially offset by a $5.0 million
increase in revenue from PG&E GT-NW's pipeline in the Pacific Northwest which
primarily resulted from higher short-term firm and interruptible revenue.

                                       11
<PAGE>
 
  OPERATING EXPENSES -  The components of total operating expenses are as
follows:


<TABLE>
<CAPTION>
                                                                   Three Months Ended                  Nine Months Ended
                                                                     September 30,                       September 30,
                                                                1998               1997              1998             1997
                                                                ----               ----              ----             ----
                                                                     (In Millions)                       (In Millions)
<S>                                                      <C>                 <C>               <C>              <C>   
Administrative and general                                 $        8.6       $        8.9      $      22.7      $       26.9
Operations and maintenance                                          3.9                5.1             11.5              13.4
Depreciation and amortization                                       9.8               10.3             29.3              31.0
Property and other taxes                                            2.8                2.8              8.8               8.6
                                                           ------------       ------------      -----------      ------------
    Total operating expenses                               $       25.1       $       27.1      $      72.3      $       79.9
                                                           ============       ============      ===========      ============
</TABLE>


  For the three and nine month periods ended September 30, 1998, compared with
the same periods in 1997, operating expenses decreased $2.0 million and $7.6
million, respectively.  The decreases reflect lower operating expenses for PG&E
GT-NW's pipeline in the Pacific Northwest and the absence of the PG&E Queensland
Gas Pipeline, which incurred $1.6 million and $4.8 million of operating expenses
for the three and nine month periods ended September 30, 1997, respectively.

  OTHER INCOME AND (INCOME DEDUCTIONS) -  Other income, net of income
deductions, for the three and nine month periods ended September 30, 1998,
increased $5.6 million and $13.3 million, respectively, compared to the same
periods in 1997, primarily reflecting the absence of investment development
expenses in 1998.

  INTEREST EXPENSE -  Interest expense for the three and nine month periods
ended September 30, 1998, decreased $1.3 million and $3.8 million, respectively,
compared to the same periods in 1997.  The decrease was primarily due to the
absence of interest on debt for the PG&E Queensland Gas Pipeline, which was sold
on September 26, 1997.  During the three and nine month periods ended September
30, 1997, interest expense for the PG&E Queensland Gas Pipeline was $1.7 million
and $5.1 million, respectively.  This decrease was partially offset by higher
interest expense for PG&E GT-NW's pipeline in the Pacific Northwest primarily
due to higher long-term debt balances.

  Interest on PG&E GT-NW's long-term debt for the pipeline in the Pacific
Northwest was approximately $31.9 million for the nine month period ended
September 30, 1998 and $30.3 million for the same period in 1997.  For the nine
months ended September 30, 1998 and 1997, the average interest rate was
approximately 7.3 percent and 7.4 percent, respectively, while the average
balance of long-term debt outstanding was $583 million and $546 million,
respectively.  For the nine months ended September 30, 1997, the average
effective interest rate for the PG&E Queensland Gas Pipeline was 7.3 percent,
based upon an average long-term debt balance of $91.7 million.


LIQUIDITY AND CAPITAL RESOURCES
-------------------------------

  SOURCES OF CAPITAL - The Company's capital requirements are funded from cash
provided by operations and, to the extent necessary, external financing and
capital contributions from its parent company.  PG&E GT-NW pays dividends as
part of a balanced approach to managing its capital structure, funding its
operations and capital expenditures, and maintaining appropriate cash balances.

                                       12
<PAGE>
 
  NET CASH PROVIDED BY OPERATING ACTIVITIES - For the nine months ended
September 30, 1998, net cash provided by operating activities was $94.2 million,
compared with $100.2 for the same period in 1997. The $6.0 million decrease was
primarily due to a $19.3 million decrease in the cash provided by the change in
working capital, offset in part by a $14.1 million increase in net income from
continuing operations. The decrease in cash provided by the change in working
capital primarily resulted from a refund for income taxes in the first quarter
of 1997 and from a decrease in receivables reflected in 1997.

  NET CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES - For the nine months
ended September 30, 1998 compared to the same period in 1997, net cash used in
investing activities increased $50.1 million. The increase primarily reflected
proceeds from the sale of PG&E GT-NW's investments in Australia in 1997 and
higher construction expenditures in 1998.

  NET CASH USED IN FINANCING ACTIVITIES - For the nine months ended September
30, 1998, cash used in financing activities was $106.1 million reflecting $130.0
million in dividends paid, partially offset by a $23.9 million net increase in
long-term debt. For the nine months ended September 30, 1997, cash used in
financing activities was $118.2 million resulting from a $66.2 million reduction
in long-term debt and $52.0 million of dividends paid. In October 1998, an
additional $15.0 million of dividends was paid.


YEAR 2000 COMPLIANCE
--------------------

  The Year 2000 issue exists for the Company because many software and embedded
systems use only two digits to identify a year in a date field and were
developed without considering the impact of the upcoming change in the century.
Some of these systems are critical to PG&E GT-NW's operations and business
processes and might fail or function incorrectly if not repaired or replaced
with Year 2000 ready products.  "Ready" means that the system is remediated so
that it will perform its essential functions.  "Software" is defined as both
computer programming that has been developed by the Company for its own purposes
("in-house software") and that purchased from vendors ("vendor software").
"Embedded systems" refers to both computing hardware and other electronic
monitoring, communications, and control systems that have microprocessors within
them.

  The Year 2000 project focuses on those systems that are critical to PG&E GT-
NW's business.  "Critical" is defined as those systems which the failure of
would directly and adversely affect the Company's ability to generate or deliver
its products and services or otherwise affect revenues, safety, or reliability
for such a period of time as to lead to unrecoverable consequences.  For these
critical systems, PG&E GT-NW has adopted a phased approach to address Year 2000
issues.  The primary phases include: (1) an enterprise-wide inventory, in which
systems critical to the business are identified; (2) assessment, in which
critical systems are evaluated as to their readiness to operate after December
31, 1999; (3) remediation, in which critical systems that are not Year 2000
ready are made so, either through modifications or replacement; (4) testing, in
which remediation is validated by checking the ability of the critical system to
operate within the Year 2000 time frame; and (5) certification, in which systems
are formally acknowledged to be Year 2000 ready, and acceptable for production
or operation.

  PG&E GT-NW's Year 2000 project is proceeding generally on schedule.  For in-
house and vendor software, the Company has completed the inventory phase and has
identified approximately 20 critical systems.  Additional software that requires
Year 2000 remediation may be discovered as the assessment, remediation, and
testing phases continue. PG&E GT-NW plans to complete remediation of all
identified, critical in-house software by the end of 1998, and remediation/
replacement of all identified, critical vendor software by February, 1999.

                                       13
<PAGE>
 
The Company expects to finish testing remediated in-house and vendor software by
May 1999 and expects to complete the certification phase for software by July
1999.

  PG&E GT-NW has also completed the inventory of all embedded systems and has
identified approximately 275 critical items.  Additional embedded items that
require Year 2000 repair or replacement may be discovered as the assessment,
remediation, and testing phases continue.  The Company estimates that
approximately 15 percent of these items are through the remediation phase.
Remediation of all critical embedded systems is expected to be completed by
April 1999.  PG&E GT-NW expects to finish testing of these remediated systems by
August 1999 and plans to complete the certification phase for embedded systems
by October 1999.

  PG&E GT-NW is testing remediated software and embedded systems both for
ability to handle Year 2000 dates, including appropriate leap year calculations,
and to assure that code repair has not affected the base functionality of the
code.  Software and embedded systems are tested individually and where necessary
will be tested in an integrated manner with other systems, with dates and data
advanced and aged to simulate Year 2000 operations.  Testing, by its nature
however, cannot comprehensively address all future combinations of dates and
events.  Some uncertainty will remain after testing as to the ability of code to
process future dates as well as the ability of remediated systems to work in an
integrated fashion with other systems.

  PG&E GT-NW also depends upon external parties including customers, suppliers,
business partners, gas system operators, and financial institutions to reliably
deliver its products and services.  To the extent that any of these parties
experience Year 2000 problems in their systems, the demand for and the
reliability of the Company's services may be adversely affected. The primary
phases that have been undertaken to deal with external parties are:  (1)
inventory, in which critical business relationships are identified; (2) action
planning, in which the Company develops a series of actions and a time frame for
monitoring expected compliance status; (3) assessment, in which the likelihood
of external party Year 2000 readiness is periodically evaluated; and (4)
contingency planning, in which appropriate plans are made to be ready to deal
with the potential failure of the external party to be Year 2000 ready.

  The Company has completed an inventory of external contacts and has identified
approximately 65 critical relationships.  PG&E GT-NW will soon complete the
action-planning phase for each of these entities.  Additional critical
relationships may be entered into or discovered as the process continues.
Assessment of Year 2000 readiness of these external parties will continue
through 1999.  The Company expects to complete contingency plans for each of
these critical business relationships by July 1999.

  PG&E GT-NW is developing contingency plans for its critical software or
embedded systems that may be at risk for Year 2000 repair or replacement. For
example, if the schedule lags and cannot be re-scheduled to meet certain
milestones, then the Company expects to begin an appropriate contingency
planning process. These contingency plans would be implemented as necessary if a
remediated system does not become available by the date it is needed. In
addition, as described above, PG&E GT-NW plans to develop contingency plans for
the potential failure of critical external parties to fully address their Year
2000 issues.

  PG&E GT-NW also recognizes that, given the complex interaction of today's
computing and communication systems, the Company cannot be certain that all of
its efforts to make all critical systems be Year 2000 ready will be successful.
Therefore, irrespective of the progress of the Year 2000 project, PG&E GT-NW is
preparing contingency plans for each essential business function.

                                       14
<PAGE>
 
The plans will take into account the possibility of multiple system failures,
both internal and external, due to Year 2000 effects.

  These essential business function contingency plans will build on existing
emergency and business restoration plans.  Although no definitive list of
scenarios for this planning has yet been developed, the events that are being
considered for planning purposes include increased frequency and duration of
interruptions of the power, computing, financial, and communications
infrastructure.  PG&E GT-NW expects to complete first drafts of these essential
business function contingency plans in the first quarter of 1999.  The Company
anticipates testing and revision of these plans throughout 1999.

  Due to the speculative nature of contingency planning, it is uncertain whether
the Company's contingency plans to address failure of external parties or
internal systems will be sufficient to reduce the risk of material impacts on
operations due to Year 2000 problems.

  PG&E GT-NW is currently revising and refining its procedures for tracking and
reporting costs associated with its Year 2000 effort.  From 1997 through
September 1998, the Company has spent approximately $1.3 million to assess and
remediate Year 2000 problems.  All of these costs have been expensed.

  PG&E GT-NW estimates that the future costs to address Year 2000 issues will be
approximately $5.3 million.  Approximately $1.4 million of these remaining Year
2000 costs are expected to be capitalized because they relate to the purchase
and installation of systems for general business purposes, and the remaining
$3.9 million is expected to be expensed.  As the assessment of systems continues
and as the remediation, testing, and certification phases of the compliance
effort progress, the estimated costs may change.  Further, PG&E GT-NW expects to
incur costs in the year 2000 and beyond to remediate and replace less critical
software and embedded systems.  PG&E GT-NW does not believe that the incremental
cost of addressing Year 2000 issues will have a material impact on the financial
position, results of operations, or cash flows of the Company.

  The Company's current schedule is subject to change, depending on developments
that may arise through further assessment of its systems, and through the
remediation and testing phases of the compliance effort.  Further, PG&E GT-NW's
current schedule is partially dependent on the efforts of third parties,
including vendors, suppliers, and customers.  Delays by third parties may cause
the schedule to change.  There are also risks associated with the loss of, or
the inability to locate, critical personnel to remediate and return to service
the identified critical systems.  PG&E GT-NW may fail to locate all systems
critical to its business processes that require remediation.  External
businesses may fail to be Year 2000 ready, which may lead to a substantial
reduction in demand for PG&E GT-NW's gas transportation services.

  Based on the Company's current schedule for the completion of Year 2000 tasks,
PG&E GT-NW believes its plan is adequate to secure Year 2000 readiness of
critical systems.  PG&E GT-NW expects its remediation efforts and those of
external parties to be largely successful.  Nevertheless, achieving Year 2000
readiness is subject to various risks and uncertainties, many of which are noted
above.  PG&E GT-NW is not able to predict all the factors that could cause
actual results to differ materially from its current expectations as to Year
2000 readiness.  If the Company, or third parties with whom the Company has
significant business relationships, fail to achieve Year 2000 readiness with
respect to critical systems, there could be a material adverse impact on PG&E
GT-NW's financial position, results of operations, and cash flows.

                                       15
<PAGE>
 
NEW ACCOUNTING  STANDARD
------------------------

  Effective January 1, 1998, the Company adopted the provisions of Statement of
Financial Accounting Standards (SFAS) No. 130, "Reporting Comprehensive Income."
SFAS No. 130 establishes standards for the reporting and display of
comprehensive income and its components in a full set of general-purpose
financial statements.  The adoption of SFAS No. 130 did not have an adverse
impact on the Company's financial position, liquidity, or results of operations.

  In June 1998, the Financial Accounting Standards Board issued Statement No.
133 "Accounting for Derivative Instruments and Hedging Activities."  The
Statement is required to be adopted in years beginning after June 15, 1999 but
permits early adoption as of the beginning of any fiscal quarter.  PG&E GT-NW
expects to adopt the new Statement no later than January 1, 2000.  The statement
will require the recognition of all derivatives, as defined in the Statement, on
the balance sheet at fair value.  Derivatives, or any portion thereof, that are
not effective hedges must be adjusted to fair value through income.  If the
derivative is an effective hedge, depending on the nature of the hedge, changes
in the fair value of derivatives either will be offset against the change in
fair value of the hedged assets, liabilities, or firm commitments through
earnings or will be recognized in other comprehensive income until the hedged
item is recognized in earnings.

  PG&E GT-NW is currently evaluating the potential impact of Statement 133 on
the earnings and financial position of the Company.

                                       16
<PAGE>
 
  PART II:  OTHER INFORMATION
  ---------------------------


ITEM 6.  EXHIBITS AND REPORTS ON FORM 8-K
         --------------------------------
 
  (a)  Exhibit 27 Financial Data Schedule for the nine months ended September
       30, 1998.

  (b)  Reports on Form 8-K during the quarter ended September 30, 1998 and
       through the date hereof:

       None.

                                       17
<PAGE>
 
                                  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.

 

                 PG&E GAS TRANSMISSION, NORTHWEST CORPORATION
                 --------------------------------------------
                                 (Registrant)



November 13, 1998       By:  /s/   STANLEY C. KARCZEWSKI
                        ----------------------------------
                        Name:   Stanley C. Karczewski
                        Title:   Vice President of Finance and Controller  
                        and Chief Financial Officer

                                       18