<PAGE>
   AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON SEPTEMBER 29, 2000

                                                      REGISTRATION NO. 333-34792
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                            ------------------------

                         POST-EFFECTIVE AMENDMENT NO. 1
                                       TO
                                    FORM S-3
                             REGISTRATION STATEMENT
                                     UNDER
                           THE SECURITIES ACT OF 1933

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

                            ENERGY EAST CORPORATION
             (Exact name of registrant as specified in its charter)

<TABLE>
<S>                                                           <C>
                          NEW YORK                                                     14-1798693
              (State or other jurisdiction of                                       (I.R.S. Employer
               incorporation or organization)                                     Identification No.)
</TABLE>

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

                                 P.O. BOX 12904
                          ALBANY, NEW YORK 12212-2904
                                 (518) 434-3049
              (Address, including zip code, and telephone number,
       including area code, of registrant's principal executive offices)

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

<TABLE>
<S>                                                           <C>
                    KENNETH M. JASINSKI                                            LEONARD BLUM, ESQ.
  Executive Vice President, General Counsel and Secretary                           FRANK LEE, ESQ.
                  Energy East Corporation                                        Huber Lawrence & Abell
                    One Canterbury Green                                            605 Third Avenue
                     Stamford, CT 06904                                            New York, NY 10158
                       (203) 325-0690                                                (212) 682-6200
       (Names, addresses, including zip codes, and telephone numbers, including area codes, of agents for service)
</TABLE>

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

                                WITH COPIES TO:
                            JOEL S. KLAPERMAN, ESQ.
                              Shearman & Sterling
                              599 Lexington Avenue
                               New York, NY 10022
                         ------------------------------

    APPROXIMATE DATE OF COMMENCEMENT OF PROPOSED SALE TO THE PUBLIC: From time
to time after the effective date of this registration statement.

    If the only securities being registered on this Form are being offered
pursuant to dividend or interest reinvestment plans, please check the following
box. / /

    If any of the securities being registered on this Form are to be offered on
a delayed or continuous basis pursuant to Rule 415 under the Securities Act of
1933, other than securities offered only in connection with dividend or interest
reinvestment plans, check the following box. /X/

    If this Form is filed to register additional securities for an offering
pursuant to Rule 462(b) under the Securities Act, check the following box and
list the Securities Act registration statement number of the earlier effective
registration statement for the same offering. / /

    If this Form is a post-effective amendment filed pursuant to Rule 462(c)
under the Securities Act, check the following box and list the Securities Act
registration statement number of the earlier effective registration statement
for the same offering. / /

    If delivery of the prospectus is expected to be made pursuant to Rule 434,
please check the following box. / /

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

    The registrant hereby amends this registration statement on such date or
dates as may be necessary to delay its effective date until the registrant files
a further amendment which specifically states that this registration statement
will then become effective in accordance with Section 8(a) of the Securities Act
of 1933 or until this registration statement becomes effective on such date as
the Securities and Exchange Commission, acting pursuant to said Section 8(a),
may determine.

--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
<PAGE>
                 SUBJECT TO COMPLETION, DATED            , 2000
THE INFORMATION IN THIS PROSPECTUS IS NOT COMPLETE AND MAY BE CHANGED. WE MAY
NOT SELL THESE SECURITIES UNTIL THE REGISTRATION STATEMENT FILED WITH THE
SECURITIES AND EXCHANGE COMMISSION IS EFFECTIVE. THIS PROSPECTUS IS NOT AN OFFER
TO SELL THESE SECURITIES AND WE ARE NOT SOLICITING AN OFFER TO BUY THESE
SECURITIES IN ANY STATE WHERE THE OFFER OR SALE IS NOT PERMITTED.
<PAGE>
PROSPECTUS

                                  $500,000,000

                            ENERGY EAST CORPORATION

                                DEBT SECURITIES

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

    We may offer to sell from time to time up to $500,000,000 in principal
amount of our notes, debentures or other unsecured debt securities in one or
more series with the same or different terms.

    We may sell the debt securities through agents, dealers or underwriters, or
directly to one or more purchasers as are designated from time to time. The debt
securities may also be sold by certain security holders. The specific terms of
each series of the debt securities will be determined at the time they are sold
and the following information will be included in a prospectus supplement:

- Total amount of debt securities offered

- Form of debt securities

- Series designation

- Agent, dealer or underwriter, if any

- Commission an agent will receive or discount a dealer or underwriter will
  receive and an estimate of the net proceeds we will receive

- Maturity date of debt securities

- Interest rates or method of calculating interest rates

- Interest payment dates

- Initial public offering price or purchase price

- Terms for repayment or redemption, if any

- Selling security holders, if any

- Any other terms applicable to the debt securities

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

    NEITHER THE SECURITIES AND EXCHANGE COMMISSION NOR ANY STATE SECURITIES
COMMISSION HAS APPROVED OR DISAPPROVED OF THESE SECURITIES OR DETERMINED IF THIS
PROSPECTUS IS TRUTHFUL OR COMPLETE. ANY REPRESENTATION TO THE CONTRARY IS A
CRIMINAL OFFENSE.

    This prospectus may not be used to sell securities unless accompanied by a
prospectus supplement.

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

                The date of this prospectus is           , 2000.
<PAGE>
                               TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                PAGE
                                                              --------
<S>                                                           <C>
ABOUT THIS PROSPECTUS.......................................       3

WHERE YOU CAN FIND MORE INFORMATION.........................       3

CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS...       4

ENERGY EAST CORPORATION.....................................       5

USE OF PROCEEDS.............................................       6

RATIO OF EARNINGS TO FIXED CHARGES..........................       7

DESCRIPTION OF DEBT SECURITIES..............................       7

SELLING SECURITY HOLDERS....................................      16

PLAN OF DISTRIBUTION........................................      16

EXPERTS.....................................................      17

LEGAL MATTERS...............................................      17
</TABLE>

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

    In this prospectus, references to "we," "us" and "our" refer to Energy East
Corporation, unless the context indicates that "we," "us" or "our" refers to
Energy East Corporation together with its consolidated subsidiaries.

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

                                       2
<PAGE>
                             ABOUT THIS PROSPECTUS

    This prospectus is part of a registration statement that we filed with the
Securities and Exchange Commission utilizing a "shelf" registration process.
Under this shelf process, any combination of the debt securities described in
this prospectus may be sold by us or certain security holders, from time to
time, in one or more offerings of one or more series. The aggregate principal
amount of debt securities which may be offered under this prospectus is
$500,000,000. This prospectus only provides you with a general description of
the securities that may be offered. Each time we, or certain security holders,
sell debt securities, we will provide a "prospectus supplement" that will
contain specific information about the terms of that offering. The prospectus
supplement may also add, update or change information contained in this
prospectus. You should read both this prospectus and any prospectus supplement
together with additional information described under the heading "Where You Can
Find More Information."

    We believe that we have included or incorporated by reference in this
prospectus all information material to investors, but certain details that may
be important for specific investment purposes have not been included. For more
detail, you should read the exhibits filed with or incorporated by reference
into the registration statement.

                      WHERE YOU CAN FIND MORE INFORMATION

AVAILABLE INFORMATION

    We file annual, quarterly and current reports, proxy statements and other
information with the SEC. You may read and copy this information at the SEC's
Public Reference Room and at its Regional Offices at:

<TABLE>
<S>                         <C>                       <C>
Public Reference Room       New York Regional Office  Chicago Regional Office
Room 1024, Judiciary Plaza  Suite 1300                Citicorp Center
450 Fifth Street, N.W.      7 World Trade Center      Suite 1400
Washington, DC 20549        New York, NY 10048        500 West Madison Street
                                                      Chicago, IL 60661-2511
</TABLE>

    You may call the SEC at 1-800-SEC-0330 for further information on the public
reference rooms. Our SEC filings are also available to the public from
commercial document retrieval services and at the Internet world wide website
that the SEC maintains at HTTP://WWW.SEC.GOV. In addition, materials and
information concerning us can be inspected at the New York Stock Exchange, 20
Broad Street, 7th Floor, New York, New York 10005, where our common stock is
listed.

    This prospectus is part of a registration statement that we filed with the
SEC. The full registration statement may be obtained from the SEC or us, as
indicated below. Forms of the indenture and any other document establishing the
terms of the offered securities are filed as exhibits to the registration
statement. Statements in this prospectus about these documents are summaries.
You should refer to the actual documents for a more complete description of the
relevant matters.

INCORPORATION BY REFERENCE

    The SEC allows us to "incorporate by reference" information into this
document, which means that we can disclose important information to you by
referring you to another document filed separately with the SEC. The information
incorporated by reference is deemed to be part of this prospectus. The
information filed with the SEC in the future will automatically update and
supersede this information.

                                       3
<PAGE>
    We incorporate by reference the documents listed below and any future
filings made by us with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the
Securities Exchange Act of 1934, until all of the debt securities being offered
under this prospectus or any prospectus supplement are sold:

    - Our Annual Report on Form 10-K for the year ended December 31, 1999.

    - Our Quarterly Reports on Form 10-Q for the quarters ended March 31, 2000
      and June 30, 2000.

    - Our Current Reports on Form 8-K filed January 31, 2000, February 8, 2000,
      February 18, 2000 and September 1, 2000.

    - Consolidated balance sheet, consolidated statement of earnings and
      consolidated statement of cash flows of CMP Group, Inc., and the notes
      related thereto, included in CMP Group's Annual Report on Form 10-K for
      the year ended December 31, 1999.

    Documents incorporated by reference are available from us without charge,
excluding all exhibits unless we have specifically incorporated by reference an
exhibit into this prospectus. You may obtain documents incorporated by reference
in this prospectus by writing or telephoning:

                            ENERGY EAST CORPORATION
                              Shareholder Services
                                 P.O. Box 3200
                          Ithaca, New York 14852-3200
                                 (607) 347-2506

    YOU SHOULD RELY ONLY ON THE INFORMATION CONTAINED OR INCORPORATED BY
REFERENCE IN THIS PROSPECTUS OR ANY PROSPECTUS SUPPLEMENT. WE HAVE NOT
AUTHORIZED ANYONE TO PROVIDE YOU WITH DIFFERENT INFORMATION. THIS PROSPECTUS IS
DATED              , 2000. WE ARE NOT MAKING AN OFFER OF THESE SECURITIES IN ANY
STATE WHERE THE OFFER IS NOT PERMITTED. YOU SHOULD NOT ASSUME THAT THE
INFORMATION CONTAINED IN THIS PROSPECTUS OR ANY PROSPECTUS SUPPLEMENT IS
ACCURATE AS OF ANY DATE OTHER THAN THE DATE OF SUCH DOCUMENTS.

           CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

    This prospectus, any accompanying prospectus supplement and the additional
information described under the heading "Where You Can Find More Information"
may contain some forward-looking statements that involve risks and
uncertainties. We may make these statements about our financial condition,
results of operations and business. You can find many of these statements by
looking for words such as "believes," "expects," "anticipates," "estimates" or
similar expressions. These forward-looking statements are subject to numerous
assumptions, risks and uncertainties. Factors that may cause actual results to
differ from those indicated by such forward-looking statements, include, among
others, the following:

    - our ability to compete in the rapidly changing and increasingly
      competitive electricity and natural gas utility markets;

    - changes in commodity supply or cost and the success of our strategies to
      satisfy power requirements now that all of our coal-fired generation
      assets have been sold;

    - our ability to control other costs;

    - the deregulation and unbundling of energy services;

    - our ability to expand our products and services, including our energy
      infrastructure in the Northeast;

                                       4
<PAGE>
    - our ability to integrate the operations of Connecticut Energy Corporation,
      CMP Group, Inc., CTG Resources, Inc. and Berkshire Energy Resources with
      our operations;

    - the ability to obtain adequate and timely rate settlements;

    - nuclear or environmental incidents;

    - legal or administrative proceedings;

    - changes in the cost or availability of capital;

    - growth in the areas in which we do business;

    - weather variations affecting customer energy usage; and

    - other considerations that may be disclosed from time to time in our
      publicly disseminated documents and filings.

    You should not place undue reliance on the forward-looking statements, which
reflect circumstances only as of the date of this prospectus or any prospectus
supplement or, in the case of a document incorporated by reference, the date of
that document.

    The cautionary statements in this section expressly qualify, in their
entirety, all subsequent forward-looking statements attributable to us or any
person acting on our behalf. We do not undertake any obligation to release
publicly any revisions to the forward-looking statements to reflect events or
circumstances occurring after the date of this prospectus, any prospectus
supplement or documents incorporated by reference.

                            ENERGY EAST CORPORATION

    We are a public utility holding company organized under the laws of the
State of New York in 1997. We are a super-regional energy services and delivery
company with operations in New York, Connecticut, Massachusetts, Maine, New
Hampshire and New Jersey and offices in New York, Connecticut and Maine. On
May 1, 1998, we became the parent of New York State Electric & Gas Corporation.
On February 8, 2000, we completed our merger with Connecticut Energy, which is a
holding company primarily engaged in the retail distribution of natural gas in
Connecticut through its wholly-owned subsidiary, The Southern Connecticut Gas
Company. On September 1, 2000, we completed our mergers with CMP Group, CTG
Resources, and Berkshire Energy. CMP Group is a holding company and its
principal utility subsidiary, Central Maine Power Company, is primarily engaged
in transmitting and distributing electricity generated by others to retail
customers in Maine. CTG Resources, also a holding company, is the parent company
of Connecticut Natural Gas Corporation, a regulated local natural gas
distribution company in Connecticut. Berkshire Energy is a holding company and
the parent company of The Berkshire Gas Company, a regulated local natural gas
distribution company in Massachusetts.

    Our principal business is purchasing, transmitting and distributing
electricity in New York and Maine and purchasing, transporting and distributing
natural gas in New York, Connecticut, Maine and Massachusetts. We generate
electricity from our nuclear and hydroelectric stations. Our New York service
territory, 99% of which is located outside the corporate limits of cities, is in
the central, eastern and western parts of the state. One of our Connecticut
service territories extends along the southern Connecticut coast from Westport
to Old Saybrook and the other is located principally in the Hartford-New Britain
area and Greenwich. Our Maine service territory is located in the southern and
central areas of the state and our Massachusetts service territory is in the
western area of that state. The approximate areas and populations of our service
territories are: New York - 19,900 square miles and 2.5 million people, Maine -
11,000 square miles and 1 million people, Connecticut

                                       5
<PAGE>
-1,318 square miles and 1.5 million people, and Massachusetts - 850 square miles
and 190,000 people. The larger cities in New York in which we serve both
electricity and natural gas are Binghamton, Elmira, Auburn, Geneva, Ithaca and
Lockport. In Connecticut the larger cities in which we serve natural gas are
Bridgeport, New Haven, Greenwich and Hartford. In Maine we serve electricity to
the city of Portland and the Lewiston-Auburn, Augusta-Waterville and
Bath-Brunswick areas, and in Massachusetts the larger cities in which we serve
natural gas are Pittsfield and North Adams. We serve approximately 1.4 million
electricity customers and 600,000 natural gas customers. Our service territories
reflect diversified economies, including high-tech firms, light industry,
colleges and universities, agriculture and recreational facilities. No customer
accounts for 5% or more of either electric or natural gas revenues.

    Our executive offices are located at One Canterbury Green, Stamford,
Connecticut 06904 where our telephone number is (203) 325-0690 and P.O. Box
12904, Albany, New York 12212-2904 where our telephone number is
(518) 434-3049.

                                USE OF PROCEEDS

    Unless otherwise specified in the supplement which accompanies this
prospectus, we intend to use the net proceeds from the sale of the debt
securities to refund certain debt securities which were used to fund a portion
of the cash consideration for the three mergers with CMP Group, CTG Resources
and Berkshire Energy. We may also invest funds not immediately required for such
purposes in short-term investment grade securities. The amount and timing of
sales of the debt securities will depend on market conditions and the
availability of other funds. We will not receive any proceeds from the sale of
securities by any selling security holders.

                                       6
<PAGE>
                       RATIO OF EARNINGS TO FIXED CHARGES

    The following table sets forth our consolidated ratio of earnings to fixed
charges for the six months ended June 30, 2000, and the five most recent fiscal
years:

<TABLE>
<CAPTION>
                                     SIX MONTHS
                                        ENDED                        ENDED DECEMBER 31,
                                      JUNE 30,     -------------------------------------------------------
                                        2000         1999          1998       1997       1996       1995
                                     -----------   --------      --------   --------   --------   --------
<S>                                  <C>           <C>           <C>        <C>        <C>        <C>
Ratio of earnings to fixed
  charges(1).......................     4.75(2)      4.14(3)       3.43       3.15       3.02       2.89
</TABLE>

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

(1) The ratio of earnings to fixed charges is calculated by dividing earnings by
    fixed charges. For this purpose earnings means income from continuing
    operations before income taxes and fixed charges. Fixed charges means all
    interest charges, the interest component of rentals and preferred stock
    dividends of subsidiaries.

(2) Due to the seasonal nature of our operations, financial results for interim
    periods are not necessarily indicative of trends for a twelve-month period.

(3) Earnings before income taxes and fixed charges includes $84 million that we
    paid in federal income taxes as a result of the sale of our coal-fired
    generation assets. Excluding the $84 million, the ratio of earnings to fixed
    charges would have been 3.52.

                         DESCRIPTION OF DEBT SECURITIES

    The following description sets forth the general terms and provisions of the
debt securities that we may offer by this prospectus. The debt securities are
senior debt securities and will rank equally with all of our other unsecured and
unsubordinated debt.

    The debt securities will be issued under an indenture between us and The
Chase Manhattan Bank, as trustee. The indenture gives us broad authority to set
the particular terms of each series of debt securities, including the right to
modify certain of the terms contained in the indenture. The particular terms of
a series of debt securities and the extent, if any, to which the particular
terms of the issue modify the terms of the indenture will be described in the
prospectus supplement relating to the debt securities.

    The indenture contains the full text of the matters described in this
section. Because this section is a summary, it does not describe every aspect of
the debt securities or the indenture. This summary is subject to and qualified
in its entirety by reference to all of the provisions of the indenture,
including definitions of terms used in the indenture. We also include references
in parentheses to certain sections of the indenture. Whenever we refer to
particular sections or defined terms of the indenture in this prospectus or in a
prospectus supplement, these sections or defined terms are incorporated by
reference herein or in the prospectus supplement. This summary also is subject
to and qualified by reference to the description of the particular terms of the
debt securities described in the applicable prospectus supplement or
supplements.

    Prospective purchasers of debt securities should be aware that special U.S.
federal income tax, accounting and other considerations may be applicable to the
debt securities of a particular series. The prospectus supplement relating to an
issue of debt securities will describe these considerations, if they apply.

    There is no requirement under the indenture that future issues of our debt
securities be issued under the indenture. We will be free to use other
indentures or documentation, containing provisions different from those included
in the indenture or applicable to one or more issues of debt securities, in
connection with future issues of other debt securities.

                                       7
<PAGE>
GENERAL

    The indenture does not limit the aggregate principal amount of debt
securities that we may issue under the indenture. The indenture provides that
the debt securities may be issued in one or more series. The debt securities may
be issued at various times and may have differing maturity dates and may bear
interest at differing rates. We need not issue all debt securities of one series
at the same time and, unless otherwise provided, we may reopen a series, without
the consent of the holders of the debt securities of that series, for issuances
of additional debt securities of that series.

    Prior to the issuance of each series of debt securities, the terms of the
particular securities will be specified in a supplemental indenture, a board
resolution or in one or more officer's certificates authorized pursuant to a
board resolution. We refer you to the applicable prospectus supplement for a
description of the following terms of the series of debt securities:

    - title of the debt securities;

    - any limit on the aggregate principal amount of the debt securities;

    - the person to whom any interest on the debt securities shall be payable,
      if other than the person in whose name the debt securities are registered
      at the close of business on the regular record date;

    - the date or dates on which the principal of the debt securities will be
      payable or how the date or dates will be determined;

    - the rate or rates at which the debt securities will bear interest, or how
      the rate or rates will be determined and the date or dates from which
      interest will accrue;

    - the dates on which interest will be payable;

    - the record dates for payments of interest;

    - the place or places, if any, in addition to the office of the trustee,
      where the principal of, and premium, if any, and interest, if any, on the
      debt securities will be payable;

    - the period or periods within which, the price or prices at which, and the
      terms and conditions upon which, the debt securities may be repaid, in
      whole or in part, at the option of the holder thereof;

    - any sinking fund or other provisions or options held by holders of the
      debt securities that would obligate us to repurchase or redeem the debt
      securities;

    - the percentage, if less than 100%, of the principal amount of the debt
      securities that will be payable if the maturity of the debt securities is
      accelerated;

    - any changes or additions to the events of default under the indenture or
      changes or additions to our covenants under the indenture;

    - any collateral, security, assurance or guarantee for the debt securities;
      and

    - any other specific terms applicable to the debt securities.

    Unless we otherwise indicate in the applicable prospectus supplement, the
debt securities will be denominated in United States currency in minimum
denominations of $1,000 and multiples of $1,000.

    Unless we otherwise indicate in the applicable prospectus supplement, there
are no provisions in the indenture or the debt securities that require us to
redeem, or permit the holders to cause a redemption of, the debt securities or
that otherwise protect the holders in the event that we incur

                                       8
<PAGE>
substantial additional indebtedness, whether or not in connection with a change
in control of our company.

SECURITY AND RANKING

    We conduct our operations primarily through our subsidiaries and
substantially all of our consolidated assets are held by our subsidiaries.
Accordingly, our cash flow and our ability to meet our obligations under the
debt securities are largely dependent upon the earnings of our subsidiaries and
the distribution or other payment of these earnings to us in the form of
dividends or loans or advances and repayment of loans and advances from us. Our
subsidiaries are separate and distinct legal entities and have no obligation to
pay any amounts due on our debt securities or to make any funds available for
payment of amounts due on our debt securities.

    Because we are a holding company, our obligations under the debt securities
will be effectively subordinated to all existing and future liabilities of our
subsidiaries. Therefore, our rights and the rights of our creditors, including
the rights of the holders of our debt securities, to participate in the assets
of any subsidiary will be subject to the prior claims of the subsidiary's
creditors. To the extent that we may be a creditor with recognized claims
against any of our subsidiaries, our claims would still be effectively
subordinated to any security interest in, or mortgages or other liens on, the
assets of the subsidiary and would be subordinated to any indebtedness or other
liabilities of the subsidiary senior to that held by us.

PAYMENT AND PAYING AGENTS

    Unless otherwise indicated in a prospectus supplement, we will pay interest
on our debt securities on each interest payment date by check mailed to the
person in whose name the debt security is registered as of the close of business
on the regular record date relating to the interest payment date, except that
interest payable at stated maturity, upon redemption or otherwise, will be paid
to the person to whom principal is paid. However, if we default in paying
interest on a debt security, we will pay defaulted interest to the registered
owner of the debt security in one of the following ways:

    - we will first propose to the trustee a payment date for the defaulted
      interest. Next, the trustee will choose a special record date for
      determining which registered holders are entitled to the payment. The
      special record date will be between 10 and 15 days before the payment date
      we propose. Finally, we will pay the defaulted interest on the payment
      date to the registered holder of the debt security as of the close of
      business on the special record date; or

    - we can propose to the trustee any other lawful manner of payment that is
      consistent with the requirements of any securities exchange on which the
      debt securities may be listed for trading. If the trustee thinks the
      proposal is practicable, payment will be made as proposed.

REDEMPTION

    We will set forth any terms for the redemption of debt securities in a
prospectus supplement. Unless we indicate differently in a prospectus
supplement, and except with respect to debt securities redeemable at the option
of the registered holder, debt securities will be redeemable upon notice by mail
between 30 and 60 days prior to the redemption date. If less than all of the
debt securities of any series or any tranche of a series are to be redeemed, the
trustee will select the debt securities to be redeemed and will choose the
method of random selection it deems fair and appropriate. (See Sections 301,
1103 and 1104.)

                                       9
<PAGE>
    Debt securities will cease to bear interest on the redemption date. We will
pay the redemption price and any accrued interest to the redemption date once
you surrender the debt security for redemption. (See Section 1106.) If only part
of a debt security is redeemed, the trustee will deliver to you a new debt
security of the same series for the remaining portion without charge. (See
Section 1107.)

    We may make any redemption conditional upon the receipt by the paying agent,
on or prior to the date fixed for redemption, of money sufficient to pay the
redemption price. If the paying agent has not received the money by the date
fixed for redemption, we will not be required to redeem the debt securities.
(See Section 1104.)

REGISTRATION, TRANSFER, EXCHANGE AND FORM

    The debt securities will be issued only in fully registered form, without
interest coupons and in denominations that are even multiples of $1,000. Debt
securities of any series will be exchangeable for other debt securities of the
same series of any authorized denominations and of a like aggregate principal
amount and tenor. (See Section 305.)

    Unless we otherwise indicate in the applicable prospectus supplement, debt
securities may be presented for registration of transfer, duly endorsed or
accompanied by a duly executed written instrument of transfer, at the office or
agency maintained for such purpose, without service charge except for
reimbursement of taxes and other governmental charges as described in the
indenture. (See Section 305.)

    In the event of any redemption of debt securities of any series, the trustee
will not be required to exchange or register a transfer of any debt securities
of the series selected, called or being called for redemption except the
unredeemed portion of any debt security being redeemed in part. (See
Section 305.)

BOOK-ENTRY ONLY SYSTEM

    The following discussion pertains to debt securities that are issued in
book-entry only form.

    One or more global notes would be issued to DTC, The Depository Trust
Company, or its nominee. DTC would keep a computerized record of its
participants (for example, your broker) whose clients have purchased the debt
securities. The participant would then keep a record of its clients who
purchased the debt securities. A global note may not be transferred, except that
DTC, its nominees and their successors may transfer an entire global note to one
another.

    Under book-entry only, we will not issue certificates to individual holders
of the debt securities. Beneficial interests in global notes will be shown on,
and transfers of beneficial interests in global notes will be made only through,
records maintained by DTC and its participants.

    DTC has advised us that it is:

    - a limited-purpose trust company organized under the New York Banking Law;

    - a "banking organization" within the meaning of the New York Banking Law;

    - a member of the Federal Reserve System;

    - a "clearing corporation" within the meaning of the New York Uniform
      Commercial Code; and

    - a "clearing agency" registered pursuant to the provisions of Section 17A
      of the Securities Exchange Act of 1934.

    DTC holds securities that its participants deposit with DTC. DTC also
facilitates the settlement among direct participants of securities transactions,
such as transfers and pledges, in deposited

                                       10
<PAGE>
securities through computerized records for direct participants' accounts. This
eliminates the need to exchange certificates. Direct participants include
securities brokers and dealers, banks, trust companies, clearing corporations
and certain other organizations.

    DTC's book-entry system is also used by other organizations such as
securities brokers and dealers, banks and trust companies that work through a
direct participant. The rules that apply to DTC and its participants are on file
with the SEC.

    DTC is owned by a number of its direct participants and by the New York
Stock Exchange, Inc., the American Stock Exchange, Inc. and the National
Association of Securities Dealers, Inc.

    We will wire principal and interest payments to DTC's nominee. We and the
trustee will treat DTC's nominee as the owner of the global notes for all
purposes. Accordingly, we and the trustee will have no direct responsibility or
liability to pay amounts due on the debt securities to owners of beneficial
interests in the global notes.

    It is DTC's current practice, upon receipt of any payment of principal or
interest, to credit direct participants' accounts on the payment date according
to their respective holdings of beneficial interests in the global notes as
shown on DTC's records as of the record date for such payment. In addition, it
is DTC's current practice to assign any consenting or voting rights to direct
participants whose accounts are credited with securities on a record date, by
using an omnibus proxy. Payments by participants to owners of beneficial
interests in the global notes, and voting by participants, will be governed by
the customary practices between the participants and owners of beneficial
interests, as is the case with securities held for the account of customers
registered in "street name." However, these payments will be the responsibility
of the participants and not of DTC, the trustee, or us.

    Debt securities represented by a global note will be exchangeable for debt
securities certificates with the same terms in authorized denominations only if:

    - DTC notifies us that it is unwilling or unable to continue as depository
      or if DTC ceases to be a clearing agency registered under applicable law;
      or

    - we instruct the trustee that the global note is now exchangeable; or

    - an event of default has occurred and is continuing.

    According to DTC, the foregoing information with respect to DTC has been
provided to the financial community for informational purposes only and is not
intended to serve as a representation, warranty, or contract modification of any
kind.

CONSOLIDATION, MERGER, CONVEYANCE, SALE OR TRANSFER

    We have agreed not to consolidate with or merge into any other entity or
convey, transfer, or lease our properties and assets substantially as an
entirety to any entity unless:

    - the successor is an entity organized and existing under the laws of the
      United States of America or any State or the District of Columbia;

    - the successor expressly assumes by a supplemental indenture the due and
      punctual payment of the principal of, and premium, if any, and interest on
      all the outstanding debt securities and the performance of every covenant
      of the indenture that we would otherwise have to perform; and

                                       11
<PAGE>
    - immediately after giving effect to the transactions, no event of default
      and no event which after notice or lapse of time or both would become an
      event of default, will have occurred and be continuing. (See
      Section 801.)

LIMITATION ON SECURED DEBT

    If this covenant is made applicable to the debt securities of any particular
series, we have agreed that we will not create, issue, incur or assume any
Secured Debt (as defined below) without the consent of the holders of a majority
in principal amount of the outstanding debt securities of all series with
respect to which this covenant is made (we refer to all such debt securities as
"Benefitted Securities"), considered as one class, provided, however, that the
foregoing covenant will not prohibit the creation, issuance, incurrence or
assumption of any debt securities by us if either:

    - we secure all Benefitted Securities then outstanding equally and ratably
      with the Secured Debt; or

    - we deliver to the Trustee bonds, notes or other evidences of indebtedness
      secured by a Lien (as defined below) which secures the Secured Debt in an
      aggregate principal amount equal to the aggregate principal amount of the
      Benefitted Securities then outstanding and meeting certain other
      requirements in the Indenture.

    "Debt" means

    - indebtedness for borrowed money evidenced by a bond, debenture, note or
      other written instrument or agreement by which we are obligated to repay
      such borrowed money; and

    - any guaranty by us of any such indebtedness of another person.

    "Lien" means any lien, deed of trust, pledge or security interest.

    "Secured Debt" means Debt created, issued, incurred or assumed by us which
is secured by a Lien upon any shares of stock of any Significant Subsidiary, as
defined in Regulation S-X of the rules and regulations under the Securities Act,
whether owned at the date of the initial authentication and delivery of the debt
securities of any series or thereafter acquired. (See Section 1007.)

MODIFICATION OF THE INDENTURE

    Under the indenture or any supplemental indenture, our rights and the rights
of the holders of debt securities may be changed with the consent of the holders
representing a majority in principal amount of the outstanding debt securities
of all series affected by the change, voting as one class, provided that the
following changes may not be made without the consent of the holders of each
outstanding debt security affected thereby:

    - change the fixed date upon which the principal of or the interest on any
      debt security is due and payable, or reduce the principal amount thereof
      or the rate of interest thereon or any premium payable upon the redemption
      thereof, or reduce the amount of the principal of an original issue
      discount security that would be payable upon a declaration of acceleration
      of the maturity thereof, or change any place of payment where, or the
      currency in which, any debt security or any premium, if any, or the
      interest thereon is payable, or impair the right to institute suit for the
      enforcement of any payment on or after the date such payment is due or, in
      the case of redemption, on or after the date fixed for such redemption;

                                       12
<PAGE>
    - reduce the stated percentage of debt securities, the consent of the
      holders of which is required for any modification of the applicable
      indenture or for waiver by the holders of certain of their rights; or

    - modify certain provisions of the indenture. (See Section 902.)

    An original issue discount security means any security authenticated and
delivered under the indenture which provides for an amount less than the
principal amount thereof to be due and payable upon the declaration of
acceleration of the maturity thereof.

    The indenture also contains provisions permitting us and the trustee to
amend the indenture in certain circumstances without the consent of the holders
of any debt securities to evidence a merger, the replacement of the trustee and
for certain other purposes. (See Section 901.)

EVENTS OF DEFAULT

    An event of default with respect to any series of debt securities is defined
in the indenture as being any one of the following:

    - failure to pay interest on the debt securities of that series for 30 days
      after payment is due;

    - failure to pay principal or any premium on the debt securities of that
      series when due;

    - failure to perform other covenants in the indenture for 60 days after we
      are given written notice from the trustee or the trustee receives written
      notice from the registered owners of at least 25% in principal amount of
      the debt securities of that series;

    - failure to pay any sinking fund installment when due;

    - default occurs under any bond, note, debenture or other instrument
      evidencing any indebtedness for money borrowed by us, excluding any of our
      subsidiaries (including a default with respect to any other series of debt
      securities issued under the indenture), or under any mortgage, indenture
      or other instrument under which there may be issued or by which there may
      be secured or evidenced any indebtedness for money borrowed by us (or the
      payment of which is guaranteed by us), excluding any of our subsidiaries,
      whether such indebtedness or guarantee exists on the date of the indenture
      or is issued or entered into following the date of the indenture, if:

       - either:

           - such default results from failure to pay any such indebtedness when
             due; or

           - as a result of such default the maturity of such indebtedness has
             been accelerated prior to its expressed maturity; and

       - the principal amount of such indebtedness, together with the principal
         amount of any other such indebtedness in default for failure to pay any
         such indebtedness when due or the maturity of which has been so
         accelerated, aggregates at least $40 million; and

    - certain events of bankruptcy, insolvency, reorganization, receivership or
      liquidation relating to us. (See Section 501.)

    An event of default regarding a particular series of debt securities does
not necessarily constitute an event of default for any other series of debt
securities.

    We will be required to file with the trustee annually an officers'
certificate as to the absence of default in performance of certain covenants in
the indenture. (See Section 1008.) The indenture provides that the trustee may
withhold notice to the holders of the debt securities of any default, except in
payment of principal of, or premium, if any, or interest on, the debt securities
or in the

                                       13
<PAGE>
payment of any sinking fund installment with respect to the debt securities, if
the trustee in good faith determines that it is in the interest of the holders
of the debt securities to do so. (See Section 602.)

    The indenture provides that, if an event of default with respect to the debt
securities specified therein shall have happened and be continuing, either the
trustee or the holders of 25% or more in aggregate principal amount of the debt
securities may declare the principal amount of all the debt securities to be due
and payable immediately. However, if we shall cure all defaults and certain
other conditions are met, such declaration may be annulled and past defaults may
be waived by the holders of a majority in aggregate principal amount of the debt
securities. (See Section 502.)

    Subject to the provisions of the indenture relating to the duties of the
trustee, the trustee will be under no obligation to exercise any of its rights
or powers under the indenture at the request or direction of any of the holders
of the debt securities, unless the holders shall have offered to the trustee
reasonable indemnity. (See Section 603.)

    Subject to the provision for indemnification, the holders of a majority in
principal amount of the debt securities will have the right to direct the time,
method and place of conducting any proceeding for any remedy available to the
trustee, or exercising any trust or power conferred on the trustee with respect
to the debt securities. However, the trustee shall have the right to decline to
follow any direction if the trustee shall determine that the action so directed
conflicts with any law or the provisions of the indenture or if the trustee
shall determine that the action would be prejudicial to holders not taking part
in the direction. (See Section 512.)

DEFEASANCE

    The indenture provides, unless otherwise provided, with respect to a
particular series of debt securities, that we may elect either (a) to be
discharged from all of our obligations with respect to the debt securities of
any series, except for obligations to register the transfer or exchange of debt
securities, replace stolen, lost or mutilated debt securities, to maintain
paying agencies and to hold moneys for payment in trust which we refer to as
"defeasance," or (b) to be released from our obligations under sections of the
indenture described under "--CONSOLIDATION, MERGER, CONVEYANCE, SALE OR
TRANSFER" and "--LIMITATION ON SECURED DEBT" or to certain covenants relating to
corporate existence and maintenance of properties and insurance, in each case,
which we refer to as "covenant defeasance," if:

    - we deposit with the trustee, in trust, money, or in certain cases, U.S.
      government obligations sufficient to pay and discharge (i) the principal
      of, and premium, if any, and interest, if any, on the outstanding debt
      securities on the dates such payments are due, in accordance with the
      terms of the debt securities and (ii) any mandatory sinking fund payments
      applicable to the debt securities on the day on which payments are due and
      payable in accordance with the terms of the indenture and of the debt
      securities;

    - no event of default or event which with notice or lapse of time would
      become an event of default, including by reason of such deposit, with
      respect to the debt securities shall have occurred and be continuing on
      the date of such deposit;

    - we deliver to the trustee an opinion of counsel to the effect that the
      holders will not recognize income, gain or loss for Federal income tax
      purposes as a result of such deposit and defeasance of certain
      obligations; and

    - we have delivered to the trustee an officers' certificate and an opinion
      of counsel, each stating that all conditions precedent provided for in the
      indenture relating to the satisfaction and discharge of the debt
      securities have been complied with. (See Sections 403 and 1009.)

                                       14
<PAGE>
    Discharged means, with respect to the debt securities of any series, the
discharge of the entire indebtedness represented by, and our obligations under,
the debt securities of such series and in the satisfaction of all of our
obligations under the indenture relating to the debt securities of such series,
except (a) the rights of holders of the debt securities of such series to
receive, from the trust fund established pursuant to the indenture, payment of
the principal of and interest and premium, if any, on the debt securities of
such series when such payments are due, (b) our obligations with respect to the
debt securities of such series with respect to registration, transfer, exchange
and maintenance of a place of payment and (c) the rights, powers, trusts,
duties, protections and immunities of the trustee under the indenture. (See
Section 101.)

    If we have deposited or caused to be deposited money or U.S. government
obligations to pay or discharge the principal of, and premium, if any, and
interest, if any, on the outstanding debt securities to and including a
redemption date on which all of the outstanding debt securities are to be
redeemed, such redemption date shall be irrevocably designated by a board of
directors resolution delivered to the trustee on or prior to the date of deposit
of such money or U.S. government obligations, and such board of directors
resolution shall be accompanied by an irrevocable company request that the
trustee give notice of such redemption in our name and at our expense not less
than 30 nor more than 60 days prior to such redemption date in accordance with
the indenture. (See Section 403.)

    U.S. government obligations means direct obligations of the United States
for the payment of which its full faith and credit is pledged, or obligations of
a person controlled or supervised by and acting as an agency or instrumentality
of the United States and the payment of which is unconditionally guaranteed by
the United States. U.S. government obligations shall also include a depositary
receipt issued by a bank or trust company as custodian with respect to any such
U.S. government obligation or a specific payment of interest on or principal of
any such U.S. government obligation held by such custodian for the account of a
holder of a depositary receipt. However, except as required by law, such
custodian is not authorized to make any deduction from the amount payable to the
holder of such depositary receipt from any amount received by the custodian in
respect of the U.S. government obligation or the specific payment of interest on
or principal of the U.S. government obligation evidenced by such depositary
receipt. (See Section 101.)

RESIGNATION OR REMOVAL OF TRUSTEE

    The trustee may resign at any time by giving written notice to us specifying
the day upon which the resignation is to take effect. The resignation will take
effect immediately upon the later of the appointment of a successor trustee and
such specified day. (See Section 610.)

    The trustee may be removed at any time by an instrument or concurrent
instruments in writing delivered to the trustee and us and signed by the
holders, or their attorneys-in-fact, representing at least a majority in
principal amount of the then outstanding debt securities. In addition, under
certain circumstances, we may remove the trustee upon notice to the holder of
each debt security outstanding and the trustee, and appointment of a successor
trustee. (See Section 610.)

CONCERNING THE TRUSTEE

    The Chase Manhattan Bank is the trustee under the indenture. Chase Manhattan
also serves as the trustee under the first mortgage bond indenture with respect
to the first mortgage bonds issued by our subsidiary, NYSEG. We maintain other
banking relationships in the ordinary course of business with the trustee and
its affiliates.

                                       15
<PAGE>
GOVERNING LAW

    The indenture and the debt securities will be governed by and construed in
accordance with the laws of the State of New York.

                            SELLING SECURITY HOLDERS

    Some of the debt securities offered by this prospectus may be offered from
time to time by existing security holders. Identification of any such selling
security holder will be made in the applicable prospectus supplement.

                              PLAN OF DISTRIBUTION

    The following methods to sell the debt securities may be used by us or the
selling security holders:

    - through negotiation with one or more underwriters;

    - through one or more agents or dealers designated from time to time;

    - directly to purchasers; or

    - through any combination of the above.

The distribution of the debt securities may be effected from time to time in one
or more transactions at a fixed price or prices which may be changed, at market
prices prevailing at the time of sale, at prices related to such prevailing
market prices or at negotiated prices. A prospectus supplement or a supplement
thereto will describe the method of distribution of any series of debt
securities.

    If any underwriters are used in the sale of debt securities, we, or the
selling security holders, as the case may be, will enter into an underwriting
agreement, distribution agreement or similar agreement with such underwriters
prior to the time of sale, and the names of the underwriters used in the
transaction will be set forth in the prospectus supplement or a supplement
thereto relating to such sale. If an underwriting agreement is executed, the
debt securities will be acquired by the underwriters for their own account and
may be resold from time to time in one or more transactions, including
negotiated transactions, at a fixed public offering price or at varying prices
determined at the time of the sale. Unless otherwise indicated in the prospectus
supplement, the underwriting or purchase agreement will provide that the
underwriter or underwriters are obligated to purchase all of the debt securities
offered in the prospectus supplement if any are purchased.

    If any debt securities are sold through agents designated by us, or the
selling security holders, as the case may be, from time to time, the prospectus
supplement or a supplement thereto will name any such agent, set forth any
commissions payable by us, or the selling security holders, as the case may be,
to any such agent and the obligations of such agent with respect to the
securities. Unless otherwise indicated in the prospectus supplement or a
supplement thereto, any such agent will be acting on a best efforts basis for
the period of its appointment.

    Certain persons participating in an offering of the debt securities may
engage in transactions that stabilize, maintain or otherwise affect the price of
the debt securities. Specifically, the underwriters, if any, may overallot in
connection with the offering, and may bid for, and purchase, the debt securities
in the open market.

    No series of debt securities, when first issued, will have an established
trading market. Any underwriters or agents to or through whom debt securities
are sold by us, or the selling security holders, as the case may be, for public
offering and sale may make a market in such debt securities, but underwriters
and agents will not be obligated to do so and may discontinue any

                                       16
<PAGE>
market making at any time without notice. No assurance can be given as to the
liquidity of the trading market for any debt securities.

    In connection with the sale of the debt securities, any purchasers,
underwriters or agents may receive compensation from us, or the selling security
holders, as the case may be, or from purchasers in the form of concessions or
commissions. The underwriters will be, and any agents and any dealers
participating in the distribution of the debt securities may be, deemed to be
underwriters within the meaning of the Securities Act of 1933. The agreement
between us, or the selling security holders, as the case may be, and any
purchasers, underwriters or agents will contain reciprocal covenants of
indemnity, and will provide for contribution by us, or the selling security
holders, as the case may be, in respect of indemnity obligations, between us, or
the selling security holders, as the case may be, and the purchasers,
underwriters, or agents against certain liabilities, including liabilities under
the Securities Act of 1933.

    Underwriters, dealers and agents may engage in transactions with, or perform
services for, us and our affiliates in the ordinary course of business.

                                    EXPERTS

    The financial statements and related financial statement schedules
incorporated in this prospectus by reference to the Annual Report on Form 10-K
of Energy East for the year
ended December 31, 1999, have been so incorporated in reliance on the report of
PricewaterhouseCoopers LLP, independent accountants, given on the authority of
said firm as experts in auditing and accounting.

    The financial statements and related financial statement schedules
incorporated in this prospectus by reference to the Annual Report on Form 10-K
of CMP Group for the year
ended December 31, 1999, have been so incorporated in reliance on the report of
PricewaterhouseCoopers LLP, independent accountants, given on the authority of
said firm as experts in auditing and accounting.

                                 LEGAL MATTERS

    The validity of the debt securities and certain other matters will be passed
upon for us by Huber Lawrence & Abell, New York, New York, and for any
underwriters, dealers or agents by Shearman & Sterling, New York, New York. As
of September 27, 2000, members of Huber Lawrence & Abell owned 4,653 shares of
our common stock.

                                       17
<PAGE>
                                    PART II
                     INFORMATION NOT REQUIRED IN PROSPECTUS

ITEM 14.  OTHER EXPENSES OF ISSUANCE AND DISTRIBUTION

    Expenses in connection with the issuance and distribution of the securities
being registered, other than underwriting compensation, are as follows:

<TABLE>
<S>                                                           <C>
SEC registration fee........................................  $132,000
Blue Sky fees and expenses..................................  $  3,500
Accounting services.........................................  $ 50,000
Printing expenses...........................................  $ 40,000
Trustee fees and expenses...................................  $ 10,000
Rating agency fees..........................................  $200,000
Legal fees and expenses.....................................  $ 80,000
Miscellaneous...............................................  $ 19,500
                                                              --------
      Total.................................................  $535,000
                                                              ========
</TABLE>

    All of the above, except the SEC registration fee, are estimated.

ITEM 15.  INDEMNIFICATION OF DIRECTORS AND OFFICERS

    The Business Corporation Law of the State of New York provides that if a
derivative action is brought against a director or officer, the registrant may
indemnify him against amounts paid in settlement and reasonable expenses,
including attorneys' fees, incurred by him in connection with the defense or
settlement of such action, if such director or officer acted in good faith for a
purpose which he reasonably believed to be in the registrant's best interests,
except that no indemnification shall be made without court approval in respect
of a threatened action, or a pending action settled or otherwise disposed of, or
in respect of any matter as to which such director or officer has been found
liable to the registrant. In a nonderivative action or threatened action, the
Business Corporation Law provides that the registrant may indemnify a director
or officer against judgments, fines, amounts paid in settlement and reasonable
expenses, including attorneys' fees incurred by him in defending such action if
such director or officer acted in good faith for a purpose which he reasonably
believed to be in the best interests of the registrant.

    Under the Business Corporation Law, a director or officer who is successful,
either in a derivative or nonderivative action, is entitled to indemnification
as outlined above. Under any other circumstances, such director or officer may
be indemnified only if certain conditions specified in the Business Corporation
Law are met. The indemnification provisions of the Business Corporation Law are
not exclusive of any other rights to which a director or officer seeking
indemnification may be entitled pursuant to the provisions of the certificate of
incorporation or the by-laws of a corporation or, whether authorized by such
certificate of incorporation or by-laws, pursuant to a shareholders' resolution,
a directors' resolution or an agreement providing for such indemnification.

    The above is a general summary of certain provisions of the Business
Corporation Law and is subject, in all cases, to the specific and detailed
provisions of Sections 721-725 of the Business Corporation Law.

    The registrant's By-Laws provide that to the extent not prohibited by law,
the registrant shall indemnify each person made, or threatened to be made, a
party to any civil or criminal action or proceeding by reason of the fact that
he, or his testator or intestate, (i) is or was a director or officer of the
registrant or (ii) is or was serving any other corporation of any type or kind,
domestic or

                                      II-1
<PAGE>
foreign, or any partnership, joint venture, trust, employee benefit plan or
other enterprise, in any capacity at the registrant's request.

    The registrant's By-Laws also provide, among other things, that:

        (1) no indemnification shall be made to or on behalf of any director or
    officer, if a judgment or other final adjudication adverse to the director
    or officer establishes that his acts were committed in bad faith or were the
    result of active and deliberate dishonesty and were material to the cause of
    action so adjudicated, or that he personally gained in fact a financial
    profit or other advantage to which he was not legally entitled;

        (2) the rights to indemnification and advancement of defense expenses
    granted by or pursuant to the By-Laws shall not limit or exclude, but shall
    be in addition to, any other rights which may be granted by or pursuant to
    any statute, certificate of incorporation, by-law, resolution or agreement;
    and

        (3) the registrant may, with the approval of its Board of Directors,
    enter into an agreement with any person who is, or is about to become, a
    director or officer of the registrant, or who is serving, or is about to
    serve, at the request of the registrant, as a director, officer, or in any
    other capacity, any other corporation of any type or kind, domestic or
    foreign, or any partnership, joint venture, trust, employee benefit plan or
    other enterprise, which agreement may provide for indemnification of such
    person and advancement of defense expenses to such person upon such terms,
    and to the extent, not prohibited by law.

    The registrant has insurance policies indemnifying its directors and
officers against certain obligations that may be incurred by them, subject to
certain retention and co-insurance provisions.

ITEM 16.  EXHIBITS

    See Exhibit Index.

ITEM 17.  UNDERTAKINGS

    The undersigned registrant hereby undertakes:

        (1) to file, during any period in which offers or sales are being made,
    a post-effective amendment to this registration statement:

           (i) to include any prospectus required by Section 10(a)(3) of the
       Securities Act of 1933;

           (ii) to reflect in the prospectus any facts or events arising after
       the effective date of the registration statement (or the most recent
       post-effective amendment thereof) which, individually or in the
       aggregate, represent a fundamental change in the information set forth in
       the registration statement. Notwithstanding the foregoing, any increase
       or decrease in volume of securities offered (if the total dollar value of
       securities offered would not exceed that which was registered) and any
       deviation from the low or high end of the estimated maximum offering
       range may be reflected in the form of prospectus filed with the
       Commission pursuant to Rule 424(b) if, in the aggregate, the changes in
       volume and price represent no more than 20% change in the maximum
       aggregate offering price set forth in the "Calculation of Registration
       Fee" table in the effective registration statement; and

           (iii) to include any material information with respect to the plan of
       distribution not previously disclosed in the registration statement or
       any material change to such information in the registration statement;

                                      II-2
<PAGE>
PROVIDED, HOWEVER, that paragraphs (i) and (ii) do not apply if the registration
statement is on Form S-3, Form S-8 or Form F-3, and the information required to
be included in a post-effective amendment by those paragraphs is contained in
periodic reports filed with or furnished to the Commission by the registrant
pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 that are
incorporated by reference in the registration statement;

        (2) that, for the purpose of determining any liability under the
    Securities Act of 1933, each such post-effective amendment shall be deemed
    to be a new registration statement relating to the securities offered
    therein, and the offering of such securities at that time shall be deemed to
    be the initial BONA FIDE offering thereof; and

        (3) to remove from registration by means of a post-effective amendment
    any of the securities being registered which remain unsold at the
    termination of the offering.

    The undersigned registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act of 1933, each filing of a
registrant's annual report pursuant to Section 13(a) or Section 15(d) of the
Securities Exchange Act of 1934 (and, where applicable, each filing of an
employee benefit plan's annual report pursuant to Section 15(d) of the
Securities Exchange Act of 1934) that is incorporated by reference in the
registration statement shall be deemed to be a new registration statement
relating to the securities offered therein, and the offering of such securities
at that time shall be deemed to be the initial BONA FIDE offering thereof.

    Insofar as indemnification for liabilities arising under the Securities Act
of 1933 may be permitted to directors, officers and controlling persons of the
registrant pursuant to the registrant's certificate of incorporation, by-laws,
the New York Business Corporation Law, or otherwise, the registrant has been
advised that in the opinion of the Commission such indemnification is against
public policy as expressed in the Securities Act of 1933 and is, therefore,
unenforceable. In the event that a claim for indemnification against such
liabilities (other than the payment by the registrant of expenses incurred or
paid by a director, officer or controlling person of the registrant in the
successful defense of any action, suit or proceeding) is asserted by such
director, officer or controlling person in connection with the securities being
registered, the registrant will, unless in the opinion of its counsel the matter
has been settled by controlling precedent, submit to a court of appropriate
jurisdiction the question whether such indemnification by it is against public
policy as expressed in the Securities Act of 1933 and will be governed by the
final adjudication of such issue.

                                      II-3
<PAGE>
                                   SIGNATURES

    Pursuant to the requirements of the Securities Act of 1933, the registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-3 and has duly caused this Post-Effective
Amendment No. 1 to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of New York, State of New York, on September 29, 2000.

<TABLE>
<S>                                                    <C>  <C>
                                                       ENERGY EAST CORPORATION

                                                       By:                /s/ FRANK LEE
                                                            -----------------------------------------
                                                                            Frank Lee
                                                                         ATTORNEY-IN-FACT
</TABLE>

    Pursuant to the requirements of the Securities Act of 1933, this
Post-Effective Amendment No. 1 has been signed by the following persons in the
capacities indicated on September 29, 2000.

<TABLE>
<CAPTION>
                      SIGNATURE                                            TITLE
                      ---------                                            -----
<S>                                                    <C>
Principal Executive, Financial and Accounting
  Officer:

                          *
     -------------------------------------------                   Chairman and Director
                Wesley W. von Schack

Directors:

                          *
     -------------------------------------------                          Director
                   Richard Aurelio

                          *
     -------------------------------------------                          Director
                  James A. Carrigg

                          *
     -------------------------------------------                          Director
                 Alison P. Casarett

                          *
     -------------------------------------------                          Director
                 Joseph J. Castiglia

                          *
     -------------------------------------------                          Director
                   Lois B. DeFleur

     -------------------------------------------                   President and Director
                  David T. Flanagan

                          *
     -------------------------------------------                          Director
                    Paul L. Gioia
</TABLE>

                                      II-4
<PAGE>

<TABLE>
<CAPTION>
                      SIGNATURE                                            TITLE
                      ---------                                            -----
<S>                                                    <C>
     -------------------------------------------                          Director
                   David M. Jagger

                          *
     -------------------------------------------                          Director
                    Ben E. Lynch

                          *
     -------------------------------------------                          Director
                   John M. Keeler

     -------------------------------------------                          Director
                  Peter J. Moynihan

                          *
     -------------------------------------------                          Director
                   Walter G. Rich

     -------------------------------------------                          Director
                 Michael W. Tomasso

                    /s/ FRANK LEE
     -------------------------------------------          As attorney-in-fact for the officers and
                      Frank Lee                                directors marked by an asterisk
</TABLE>

                                      II-5
<PAGE>
                                 EXHIBIT INDEX

<TABLE>
<CAPTION>
EXHIBIT NO.                                 DESCRIPTION                           METHOD OF FILING
-----------             ---------------------------------------------------  --------------------------
<C>                     <S>                                                  <C>
         1              Form of Underwriting Agreement.                      Previously filed.

         4-1            Form of Indenture from Energy East to The Chase      Previously filed.
                        Manhattan Bank, as Trustee.

         4-2            Form of Debt Security.                               Included in Exhibit 4-1.

         5              Opinion of Huber Lawrence & Abell with respect to    Previously filed.
                        the legality of the securities registered
                        hereunder.

        12              Computation of Ratio of Earnings to Fixed Charges.   Filed herewith.

        23-1            Consent of Huber Lawrence & Abell.                   Included in opinion filed
                                                                             as Exhibit 5.

        23-2            Consent of PricewaterhouseCoopers LLP.               Filed herewith.

        23-3            Consent of PricewaterhouseCoopers LLP.               Filed herewith.

        24-1            Powers of Attorney of Directors and Officers.        Previously filed.

        24-2            Power of Attorney of the Registrant.                 Previously filed.

        25              Statement of Eligibility and Qualification of The    Previously filed.
                        Chase Manhattan Bank as Trustee under the
                        Indenture.
</TABLE>