<PAGE>

                                    FORM 10-Q

                       SECURITIES AND EXCHANGE COMMISSION

                             WASHINGTON, D.C. 20549

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

                For the quarterly period ended December 31, 1999

                         Commission file number: 1-7196

                         CASCADE NATURAL GAS CORPORATION
             (Exact name of Registrant as specified in its charter)

                Washington                          91-0599090
                ----------                          ----------
      (State or other jurisdiction of           (I.R.S. Employer
      incorporation or organization)            Identification No.)

     222 Fairview Avenue North, Seattle, WA                   98109
     --------------------------------------                   -----
    (Address of principal executive offices)                (Zip code)

 (Registrant's telephone number including area code)       (206) 624-3900
                                                           --------------

         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 registrant's
classes of common stock, as of the latest practicable date.

                  Title                              Outstanding
                  -----                              -----------

  Common Stock, Par Value $1 per Share     11,045,095 as of January 31, 2000


<PAGE>


                         CASCADE NATURAL GAS CORPORATION
                         -------------------------------

                                      Index
<TABLE>
<CAPTION>
                                                                                           Page No.
                                                                                           -------
<S>                                                                                        <C>
Part I.  Financial Information

                  Item 1. Financial Statements

                       Consolidated Condensed Statements of Net Earnings                           3

                       Consolidated Condensed Balance Sheets                                       4

                       Consolidated Condensed Statements of Cash Flows                             5

                       Notes to Consolidated Condensed Financial Statements                        6

                  Item 2.  Management's Discussion and Analysis of Financial Condition
                               and Results of Operations                                           7

                  Item 3. Quantitative and Qualitative Disclosures about Market Risk               9


Part II. Other Information

                  Item 2. Changes in Securities                                                   10

                  Item 4. Submission of Matters to a Vote of Security Holders.                    10

                  Item 5. Other Information                                                       10

                  Item 6. Exhibits and Reports on Form 8-K                                        11

Signature                                                                                         12
</TABLE>


                                       2

<PAGE>


PART I.   FINANCIAL INFORMATION

ITEM 1.  FINANCIAL STATEMENTS



                CASCADE NATURAL GAS CORPORATION AND SUBSIDIARIES
                CONSOLIDATED CONDENSED STATEMENTS OF NET EARNINGS
                                   (unaudited)
<TABLE>
<CAPTION>

                                                                   THREE MONTHS ENDED
                                                        ---------------------------------------

                                                         Dec 31, 1999            Dec 31, 1998
                                                        ----------------         --------------
                                                           (thousands except per share data)
<S>                                                      <C>                     <C>

 Operating revenues                                           $  73,791              $  62,917

 Less: Gas purchases                                             41,869                 32,016
       Revenue taxes                                              4,314                  3,739
                                                        ----------------         --------------
 Operating margin                                                27,608                 27,162
                                                        ----------------         --------------

 Cost of operations:
      Operating expenses                                          8,545                  9,417
      Depreciation and amortization                               3,280                  3,148
      Property and payroll taxes                                  1,191                  1,159
                                                        ----------------         --------------
                                                                 13,016                 13,724
                                                        ----------------         --------------


 Earnings from operations                                        14,592                 13,438
 Less interest and other
   deductions - net                                               2,559                  2,622
                                                        ----------------         --------------
 Earnings before income taxes                                    12,033                 10,816


 Income taxes                                                     4,392                  4,062
                                                        ----------------         --------------
 Net earnings                                                     7,641                  6,754
 Preferred dividends                                                  1                    123
                                                        ----------------         --------------
 Net earnings available to
     common shareholders                                      $   7,640              $   6,631
                                                        ================         ==============

 Weighted average common shares outstanding                      11,045                 11,045

 Net earnings  per common share (basic & diluted)              $   0.69               $   0.60
                                                        ================         ==============

 Cash dividends per share                                      $   0.24               $   0.24
                                                        ================         ==============
</TABLE>

 The accompanying notes are an integral part of these financial statements


                                       3
<PAGE>

                CASCADE NATURAL GAS CORPORATION AND SUBSIDIARIES
                      CONSOLIDATED CONDENSED BALANCE SHEETS
                             (Dollars in Thousands)
<TABLE>
<CAPTION>

                                                                    Dec 31, 1999    Sep 30, 1999
                                                                   -------------    ------------
                                ASSETS                              (Unaudited)
<S>                                                               <C>                 <C>
 Utility Plant, net of accumulated
     depreciation of $180,228 and $177,878                         $  278,133          $275,400
     Construction work in progress                                      5,612             6,891
                                                                   -----------      ------------
                                                                      283,745           282,291
                                                                   -----------      ------------
 Other Assets:
     Investments in non-utility property                                  202               202
     Notes receivable, less current maturities                            517               577
                                                                   -----------      ------------
                                                                          719               779
                                                                   -----------      ------------
 Current Assets:
     Cash and cash equivalents                                          3,416               410
     Accounts receivable, less allowance of $637
       and $622  for doubtful accounts                                 32,388            12,468
     Current maturities of notes receivable                               155               176
     Materials, supplies and inventories                                6,210             6,250
     Prepaid expenses and other assets                                  7,597             5,584
                                                                   -----------      ------------
                                                                       49,766            24,888
                                                                   -----------      ------------
 Deferred Charges                                                       7,239             7,611
                                                                   -----------      ------------
                                                                     $341,469          $315,569
                                                                   ===========      ============

                   COMMON SHAREHOLDERS' EQUITY,
                 PREFERRED STOCKS AND LIABILITIES

 Common Shareholders' Equity:
     Common stock, par value $1 per share, authorized 15,000,000
      shares, issued and outstanding 11,045,095 shares               $ 11,045          $ 11,045
     Additional paid-in capital                                        97,380            97,380
     Retained earnings                                                 10,959             5,970
                                                                   -----------      ------------
                                                                      119,384           114,395
                                                                   -----------      ------------
 Redeemable Preferred Stocks, aggregate redemption
   amount of $73 and $6,338                                                62             6,186
                                                                   -----------      ------------
 Long-term Debt                                                       125,000           125,000
                                                                   -----------      ------------
 Current Liabilities:
     Notes payable and commercial paper                                10,213                 -
     Accounts payable                                                  17,592             8,933
     Property, payroll and excise taxes                                 5,569             3,434
     Dividends and interest payable                                     5,389             7,614
     Other current liabilities                                          7,786             4,527
                                                                   -----------      ------------
                                                                       46,549            24,508
                                                                   -----------      ------------
 Deferred Credits and Other:
     Gas cost changes                                                  14,499            12,210
     Other                                                             35,975            33,270
                                                                   -----------      ------------
                                                                       50,474            45,480
                                                                   -----------      ------------
 Commitments and Contingencies                                              -                 -
                                                                     $341,469          $315,569
                                                                   ===========      ============
</TABLE>
    The accompanying notes are an integral part of these financial statements

                                       4
<PAGE>

                CASCADE NATURAL GAS CORPORATION AND SUBSIDIARIES
                      CONSOLIDATED STATEMENTS OF CASH FLOWS
<TABLE>
<CAPTION>


(Dollars in thousands)                                                 THREE MONTHS ENDED
                                                                ------------------------------------

                                                                 Dec 31, 1999         Dec 31, 1998
                                                                ----------------     ---------------
                                                                 (thousands except per share data)
<S>                                                              <C>                 <C>
Operating Activities
   Net earnings                                                      $    7,641          $    6,754
   Adjustments to reconcile net earnings to
       net cash provided by operating activities:
     Depreciation and amortization                                        3,280               3,148
     Deferrals of gas cost changes                                        1,658               1,276
     Amortization of gas cost changes                                       631                  93
     Other deferrals and amortizations                                      981                 616
     Deferred income taxes and tax credits - net                            223                 253
     Other                                                                  131                   -
     Change in current assets and liabilities                           (10,083)            (12,280)
                                                                ----------------     ---------------
   Net cash provided (used) by operating activities                       4,462                (140)
                                                                ----------------     ---------------

Investing Activities
   Capital expenditures                                                  (4,353)             (6,521)
   Customer contributions in aid of construction                          1,361                 485
   Other                                                                     99                 222
                                                                ----------------     ---------------
   Net cash used by investing activities                                 (2,893)             (5,814)
                                                                ----------------     ---------------

Financing Activities
   Redemption of preferred stock                                         (6,124)               (222)
   Repayment of long-term debt                                                -             (10,000)
   Changes in notes payable and commercial paper, net                    10,213              16,785
   Dividends paid                                                        (2,652)             (2,774)
                                                                ----------------     ---------------
   Net cash provided by financing activities                              1,437               3,789
                                                                ----------------     ---------------


Net Increase (Decrease) in Cash and Cash Equivalents                      3,006              (2,165)

Cash and Cash Equivalents

   Beginning of period                                                      410               2,338
                                                                ----------------     ---------------
   End of period                                                     $    3,416           $     173
                                                                ================     ===============
</TABLE>


The accompanying  notes are an integral part of these financial statements


                                       5
<PAGE>


                         CASCADE NATURAL GAS CORPORATION
              NOTES TO CONSOLIDATED CONDENSED FINANCIAL STATEMENTS
                      THREE MONTHS ENDED DECEMBER 31, 1999

         The preceding statements were taken from the books and records of the
Company and reflect all adjustments which are, in the opinion of management,
necessary for a fair statement of the results for the interim periods. All
adjustments were of a normal and recurring nature. Because of the highly
seasonal nature of the natural gas distribution business, earnings or loss for
any portion of the year are disproportionate in relation to the full year.

         Reference is directed to the Notes to Consolidated Financial Statements
contained in the 1999 Annual Report on Form 10-K for the fiscal year ended
September 30, 1999, and comments included therein under "Management's Discussion
and Analysis of Financial Condition and Results of Operations".

NEW ACCOUNTING STANDARDS:

SOP 98-1. As of the first quarter of fiscal 2000, the Company adopted Statement
of Position (SOP) 98-1, "ACCOUNTING FOR THE COSTS OF COMPUTER SOFTWARE DEVELOPED
OR OBTAINED FOR INTERNAL USE", issued by the Accounting Standards Executive
Committee of the American Institute of Certified Public Accountants. The SOP
establishes criteria for accounting for software costs as operating expense when
incurred, or as a capital expenditure. It provides that internal and external
costs incurred to develop or obtain new software during the "application
development stage" should be capitalized. Other costs, including preliminary
project costs, training, data conversion, and upgrades and enhancements, would
be expensed under the provisions of SOP 98-1. The significance of this change is
dependent upon the magnitude of the costs and the nature and complexity of
specific software development or acquisition projects incurred in any period.
For the quarter ended December 31, 1999, adoption of this standard affected the
accounting for the costs of one of the Company's software projects. During the
quarter, this project was in the application development stage. As a result of
adopting SOP 98-1, the Company capitalized $18,000 which would have been
expensed under its previous policy. These costs were primarily internal labor.

FAS NO. 133. In June 1998, the Financial Accounting Standards Board issued FAS
No. 133, entitled "ACCOUNTING FOR DERIVATIVE INSTRUMENTS AND HEDGING
ACTIVITIES." This standard will be effective for fiscal years beginning after
June 15, 2000, and will be adopted by the Company as of October 1, 2000. It
requires that the fair value of all derivative financial instruments be
recognized as either assets or liabilities on the Company's balance sheet.
Changes during a period in the fair value of a derivative instrument would be
included in earnings or other comprehensive income for the period.

         The Company is currently evaluating the effects of this standard on its
financial reporting. This evaluation is not complete, but the Company believes
that some of its natural gas supply contracts may meet the technical definition
of derivative instruments, and thus may be subject to the requirements of FAS
No. 133. The Company also believes that, because of rate regulation, derivative
assets and liabilities may be offset by regulatory assets and regulatory
liabilities, and the earnings effect of application of this standard will not be
material.


                                       6
<PAGE>


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

         The following is management's assessment of the Company's financial
condition and a discussion of the principal factors that affected consolidated
results of operations and cash flows for the three month periods ended December
31, 1999 and December 31, 1998.

RESULTS OF OPERATIONS

         Net earnings available to common shareholders for the first quarter of
fiscal 2000 (quarter ended December 31, 1999) was $7,640,000, or $0.69 per
share, compared to $6,631,000, or $0.60 per share, for the quarter ended
December 31, 1998. This represents a 15% improvement in first quarter earnings
per share over first quarter 1999 results. Improvements in results for the
quarter are primarily attributable to increases in operating margins and lower
operating expenses.

OPERATING MARGIN

         RESIDENTIAL AND COMMERCIAL MARGIN. Operating margins derived from sales
to residential and commercial customers were as set forth in the following
table:

<TABLE>
<CAPTION>

                    RESIDENTIAL AND COMMERCIAL OPERATING MARGIN
             ----------------------------------------------------------
                                    First Quarter of Fiscal    Percent
                                       2000         1999       Change
             ----------------------------------------------------------
                                   (dollars in thousands)

             <S>                      <C>          <C>          <C>
             DEGREE DAYS                 1,942        2,015      (3.6)%
             AVERAGE NUMBER OF
              CUSTOMERS
                Residential            155,119      147,710       5.0%
                Commercial              26,892       25,989       3.5%
             AVERAGE THERM USAGE PER
              CUSTOMER
                Residential                267          281      (5.0)%
                Commercial               1,416        1,359       4.2%
             OPERATING MARGIN
                 Residential          $ 11,595     $ 11,458       1.2%
                Commercial             $ 7,267      $ 7,193       1.0%
</TABLE>

         For the quarter ended December 31, 1999, operating margin from sales
to residential and commercial customers increased $211,000 from the same period
last year. The addition of 8,300 new customers provided approximately $912,000
margin. Lower usage per residential customer, and higher revenue taxes were the
primary factors partially offsetting this improvement.

         INDUSTRIAL AND OTHER MARGIN. Operating margin from industrial and other
customers increased $256,000, or 3.1%, quarter to quarter. Increased gas
consumption by customers in various industrial classifications, as well as the
addition of several smaller industrial customers, contributed to this increase.

COST OF OPERATIONS

         Cost of operations for the quarter ended December 31, 1999, which
consists of operating expenses, depreciation and amortization, and property and
payroll taxes, decreased $708,000 or 5.2% from the quarter ended December 31,
1998.

         OPERATING EXPENSES, which are primarily labor and benefits expenses,
decreased by $872,000, or 9.3%, for the quarter. A $394,000, or 6.4%, reduction
in labor expense was the most significant factor. The Company's workforce
decreased by 27 employees (5.6%) compared to the December 1998 quarter,
reflecting ongoing efforts to increase operating efficiencies. Employee benefits
expense increased $134,000 (5.4%) mainly as a result of higher medical costs.
Most other categories of expense decreased.


                                       7
<PAGE>


Also affecting the quarterly comparison was $98,000 in one-time costs associated
with management restructuring, recorded in the December 1998 quarter.

         DEPRECIATION AND AMORTIZATION increased $132,000, or 4.2%, for the
quarter ended December 31, 1999 compared to the same period a year earlier, as a
result of increases in depreciable assets.

         PROPERTY AND PAYROLL TAXES increased $32,000, or 2.8%, for the December
1999 quarter compared to a year earlier. Decreases in payroll taxes resulting
from lower staffing levels were more than offset by property tax increases.

INTEREST AND OTHER DEDUCTIONS - NET

         Interest and other deductions - net, for the quarter was $2,559,000, a
$63,000 reduction from the December 1998 quarter. Included in the December 1999
quarter was a $131,000 credit for the gain on the sale of surplus property.

LIQUIDITY AND CAPITAL RESOURCES

         The seasonal nature of the Company's business creates short-term cash
requirements to finance customer accounts receivable and construction
expenditures. To provide working capital for these requirements, the Company has
a revolving credit commitment of $40 million from a bank. This agreement expires
in 2004. The annual commitment fee is 1/8 of 1%, and is subject to change based
on the ratings assigned to the Company's long-term debt. The committed lines of
credit also support a $25 million commercial paper facility. The Company also
has $30 million of uncommitted lines from three banks.

         A Medium-Term Note program provides longer term financing, with $125
million outstanding at December 31, 1999. There is remaining $15 million
registered under the Securities Act of 1933 and available for issuance. Because
of the availability of short-term credit and the ability to issue long-term debt
and additional equity, management believes it has adequate financial flexibility
to meet its anticipated cash needs.

OPERATING ACTIVITIES

         Net cash provided by operating activities was $4,462,000 for the
December 1999 quarter, compared to a net use of cash of $140,000 for the same
period last year. The primary factors contributing to this improvement were the
higher earnings for the quarter, and lower seasonal working capital
requirements.

INVESTING ACTIVITIES

         Cash used by investing activities for the quarter ended December 31,
1999 was $2,893,000, compared to $5,814,000 for the prior year's quarter. The
comparison is affected by lower capital expenditures and higher customer
contributions in the first quarter of fiscal 2000.

         Capital expenditures for fiscal 2000 are budgeted at approximately
$23.5 million, which is expected to be financed approximately 75% from operating
activities and 25% from debt financing.

FINANCING ACTIVITIES

         Net financing activities for the quarter ended December 31, 1999
provided $1,437,000, compared to $3,789,000 for the comparable period last year.
During the first quarter of fiscal 2000, the Company redeemed $6.1 million of
preferred stock, which matured in November 1999. This redemption was funded with
short-term debt.


                                       8
<PAGE>


YEAR 2000 READINESS DISCLOSURE

The Company did not experience any material disruptions in its computer systems
during the transition to year 2000. No year 2000 problems were reported to the
Company by any of its customers or suppliers that would have a material effect
on its business with them.

COSTS OF YEAR 2000 COMPLIANCE. The Company used a combination of internal and
external resources to make necessary modifications to existing computer systems.
The Company did not separately track the direct cost associated with internal
personnel assigned to the Year 2000 project. Costs associated with using
internal resources were viewed primarily as opportunity costs, resulting in
delays of other planned system enhancements. Such delays and enhancements are
not expected to have a material adverse effect on the Company or its competitive
position. The Company's total capital expenditures to replace non-compliant
systems have been approximately $1.4 million. Total external costs for Year 2000
compliance charged to operating expense were less than $100,000.



ITEM 3.  QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK

         The Company has evaluated its risk related to financial instruments
whose values are subject to market sensitivity. The only such instruments are
Company-issued fixed-rate debt obligations. The Company makes interest and
principal payments on these obligations in the normal course of its business,
and does not plan to redeem these obligations prior to normal maturities.
Accordingly, management believes the Company is not subject to market risk as
defined in Item 305 of Regulation S-K.



FORWARD LOOKING STATEMENTS

         Statements contained in this report that are not historical in nature
are forward-looking statements within the meaning of the Private Securities
Litigation Reform Act of 1995. Forward-looking statements are subject to risks
and uncertainties that may cause actual future results to differ materially.
Such risks and uncertainties with respect to the Company include, among others,
its ability to successfully implement internal performance goals, competition
from alternative forms of energy, consolidation in the energy industry,
performance issues with key natural gas suppliers, the capital-intensive nature
of the Company's business, regulatory issues, including the need for adequate
and timely rate relief to recover increased capital and operating costs
resulting from customer growth and to sustain dividend levels, the weather,
increasing competition brought on by deregulation initiatives at the federal and
state regulatory levels, the potential loss of large volume industrial customers
due to "bypass" or the shift by such customers to special competitive contracts
at lower per unit margins, exposure to environmental cleanup requirements, and
economic conditions, particularly in the Company's service area.


                                       9
<PAGE>


PART II.  OTHER INFORMATION

ITEM 2.  CHANGES IN SECURITIES

         Under the terms of its bank credit agreement, the Company is required
to maintain a minimum net worth of $101,357,000 as of December 31, 1999. Under
this agreement, approximately $12,660,000 was available for payment of dividends
at December 31, 1999.

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

         At the annual meeting of shareholders on January 27, 2000, the
following directors were elected by the vote indicated for terms of office
expiring in 2001:

<TABLE>
<CAPTION>

                                 For                     Withheld
                           ---------------             ------------
<S>                        <C>                          <C>
 Carl Burnham, Jr.              9,401,627                  129,468
 Melvin C. Clapp                9,399,951                  131,144
 Thomas E. Cronin               9,392,741                  138,354
 David A. Ederer                9,395,178                  135,917
 Howard L. Hubbard              9,394,173                  136,922
 W. Brian Matsuyama             9,395,651                  135,444
 Larry L. Pinnt                 9,390,543                  140,552
 Brooks G. Ragen                9,397,433                  133,662
 Mary A. Williams               9,397,065                  134,030
</TABLE>


  ITEM 5.  OTHER INFORMATION

Ratio of Earnings to Fixed Charges:

<TABLE>
<CAPTION>

                          Twelve Months Ended
 -----------------------------------------------------------------------
 12/31/1999   9/30/1999   9/30/1998    9/30/1997   9/30/1996   9/30/1995
 ----------   ---------   ---------    ---------   ---------   ---------
<S>           <C>         <C>          <C>         <C>         <C>
    3.10         3.00        2.42         2.68        2.17        2.16
</TABLE>


         For purposes of this calculation, earnings include income before income
taxes, plus fixed charges. Fixed charges include interest expense and the
amortization of debt issuance expenses. Refer to Exhibit 12 for the calculation
of these ratios, as well as the ratio of earnings to fixed charges including
preferred dividends.


                                       10
<PAGE>


ITEM 6.  EXHIBITS AND REPORTS ON FORM 8-K

a. Exhibits:

         No.                        Description
         ---                        -----------

          12               Computation of Ratio of Earnings to Fixed Charges

          27               Financial Data Schedule UT

b. Reports on Form 8-K:

                   No reports were filed on Form 8-K during the quarter ended
December 31, 1999.

                                       11
<PAGE>


SIGNATURE

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.

CASCADE NATURAL GAS CORPORATION

By:                /s/  J. D.  Wessling
            --------------------------------


                       J. D. Wessling
       Sr. Vice President Finance and Chief Financial Officer
                 (Principal Financial Officer)


Date:                February 10, 2000
            --------------------------------