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                                                                     EXHIBIT 5.1

                       [SCHIFF HARDIN & WAITE LETTERHEAD]





                                                     April 21, 2000




NiSource Inc.                                        New NiSource Inc.
801 East 86th Avenue                                 801 East 86th Avenue
Merrillville, Indiana 46410                          Merrillville, Indiana 46410

                  RE: REGISTRATION STATEMENT ON FORM S-4

Ladies and Gentlemen:

                  We have acted as counsel to NiSource Inc., an Indiana
corporation ("NiSource"), and New NiSource Inc., a Delaware corporation ("New
NiSource"), in connection with their filing of a Registration Statement on Form
S-4 and Amendment No. 1 thereto (the "Registration Statement") under the
Securities Act of 1933, as amended (the "Securities Act"), with respect to the
registration of the following securities that may be issued pursuant to the
Agreement and Plan of Merger dated as of February 27, 2000, as amended and
restated as of March 31, 2000, among NiSource, Columbia Energy Group
("Columbia"), New NiSource, Parent Acquisition Corp., Company Acquisition Corp.
and NiSource Finance Corp. (the "Merger Agreement"): (i) Common Shares of New
NiSource, $.01 par value, including related Share Purchase Rights (the "New
NiSource Common Shares"); (ii) Share Purchase Contracts of New NiSource (the
"New NiSource Share Purchase Contracts"); (iii) Debt Securities of New NiSource
(the "New NiSource Debt Securities"); (iv) New NiSource Share Purchase Units,
consisting of the New NiSource Share Purchase Contracts and the New NiSource
Debt Securities or U.S. Treasury securities; (v) Share Purchase Contracts of
NiSource (the "NiSource Share Purchase Contracts"); (vi) Debt Securities of
NiSource (the "NiSource Debt Securities"); (vii) NiSource Share Purchase Units,
consisting of the NiSource Share Purchase Contracts and the NiSource Debt
Securities or U.S. Treasury securities; and (viii) Common Shares of NiSource,
without par value, including related Share Purchase Rights (the "NiSource Common
Shares").



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                  In connection with our opinion, we have examined the
Registration Statement, including the exhibits thereto, and such other
documents, corporate records and instruments, and have examined such laws and
regulations, as we have deemed necessary for the purposes of this opinion. In
such examination, we have assumed the genuineness of all signatures, the
authenticity of all documents submitted to us as originals, the conformity to
the original documents of all documents submitted to us as copies and the
authenticity of the originals of such latter documents.

                  On the basis of such examination, we are of the opinion that,
when the Registration Statement, as it may be amended, has become effective
under the Securities Act and any applicable state securities or Blue Sky laws
have been complied with:

                  1. The New NiSource Share Purchase Contracts will be valid and
legally binding obligations of New NiSource, subject to bankruptcy, insolvency,
fraudulent transfer, reorganization, moratorium and similar laws of general
applicability relating to or affecting creditors' rights and to general equity
principles at such time as: (i) the Purchase Contract Agreement between New
NiSource and The Chase Manhattan Bank, as purchase contract agent, has been duly
executed and delivered; (ii) the merger of Company Acquisition Corp. into
Columbia has been consummated as provided in the Merger Agreement; and (iii) the
New NiSource Share Purchase Contracts have been duly executed and delivered as
required by the Merger Agreement and contemplated by the Registration Statement.

                  2. The New NiSource Common Shares that are to be issued in
exchange for Columbia common shares as provided in the Merger Agreement have
been duly authorized and will be validly issued, fully paid, and nonassessable
at such time as: (i) the Share Purchase Rights Agreement between New NiSource
and the rights agent, with respect to the Share Purchase Rights included in the
New NiSource Common Shares, has been duly executed and delivered; (ii) the
merger of Company Acquisition Corp. into Columbia has been consummated as
provided in the Merger Agreement; and (iii) the New NiSource Common Shares have
been duly issued pursuant to elections by Columbia shareholders as contemplated
by the Merger Agreement.

                  3. The New NiSource Common Shares that are to be issued in
exchange for NiSource common shares as provided in the Merger Agreement have
been duly authorized and will be validly issued, fully paid, and nonassessable
at such time as: (i) the Share Purchase Rights Agreement between New NiSource
and the rights agent, with respect to the Share Purchase Rights included in the
New NiSource Common Shares, has been duly executed and delivered; and (ii) the
merger of Parent



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April 21, 2000
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Acquisition Corp. into NiSource has been consummated as provided in the Merger
Agreement.


                  4. The New NiSource Common Shares that are to be issued on
settlement of the New NiSource Share Purchase Contracts have been duly
authorized and will be validly issued, fully paid and nonassessable at such time
as: (i) the merger of Company Acquisition Corp. into Columbia has been
consummated as provided in the Merger Agreement; (ii) the Purchase Contract
Agreement between New NiSource and The Chase Manhattan Bank, as purchase
contract agent, has been duly executed and delivered; (iii) the New NiSource
Share Purchase Contracts have been duly executed and delivered as required by
the Merger Agreement and contemplated by the Registration Statement; (iv) the
Share Purchase Rights Agreement between New NiSource and the rights agent, with
respect to the Share Purchase Rights included in the New NiSource Common Shares,
has been duly executed and delivered; and (v) the New NiSource Share Purchase
Contracts are settled in accordance with their terms, as contemplated by the
Registration Statement.


                  5. The New NiSource Debt Securities will be valid and legally
binding obligations of New NiSource, subject to bankruptcy, insolvency,
fraudulent transfer, reorganization, moratorium and similar laws of general
applicability relating to or affecting creditor's rights and to general equity
principles at such time as: (i) the indenture, and the supplemental indenture,
each between New NiSource and The Chase Manhattan Bank, as trustee, that are
described in the Registration Statement (together, the "New NiSource Indenture")
have been duly executed and delivered; (ii) the merger of Company Acquisition
Corp. into Columbia has been consummated as provided in the Merger Agreement;
and (iii) the New NiSource Debt Securities have been duly executed and
authenticated in accordance with the New NiSource Indenture.

                  6. The New NiSource Share Purchase Units will be valid and
legally binding obligations of New NiSource, subject to bankruptcy, insolvency,
fraudulent transfer, reorganization, moratorium and similar laws of general
applicability relating to or affecting creditors' rights and to general equity
principles, at such time as the conditions set forth in paragraphs 1 and 5 of
this opinion have been satisfied.

                  7. The NiSource Share Purchase Contracts will be valid and
legally binding obligations of NiSource, subject to bankruptcy, insolvency,
fraudulent transfer, reorganization, moratorium and similar laws of general
applicability relating to or affecting creditors' rights and to general equity
principles at such time as: (i) the Purchase Contract Agreement between NiSource
and The Chase Manhattan Bank, as purchase contract agent, has been duly executed
and delivered; (ii) the merger of Company Acquisition Corp. into Columbia has
been consummated pursuant to the alternative structure described in Section 2.4
of the Merger Agreement; and (iii) the



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NiSource Share Purchase Contracts have been duly executed and delivered as
required by the Merger Agreement and contemplated by the Registration Statement.

                  8. The NiSource Common Shares that are to be issued on
settlement of the NiSource Share Purchase Contracts have been duly authorized
and will be validly issued, fully paid and nonassessable at such time as: (i)
the merger of Company Acquisition Corp. into Columbia has been consummated
pursuant to the alternative structure described in Section 2.4 of the Merger
Agreement; (ii) the Purchase Contract Agreement between NiSource and The Chase
Manhattan Bank, as purchase contract agent, has been duly executed and
delivered; (iii) the NiSource Share Purchase Contracts have been duly executed
and delivered as required by the Merger Agreement and contemplated by the
Registration Statement; and (iv) the NiSource Share Purchase Contracts are
settled in accordance with their terms, as contemplated by the Registration
Statement.

                  9. The NiSource Debt Securities will be valid and legally
binding obligations of NiSource, subject to bankruptcy, insolvency, fraudulent
transfer, reorganization, moratorium and similar laws of general applicability
relating to or affecting creditor's rights and to general equity principles at
such time as: (i) the indenture, and the supplemental indenture, each between
NiSource and The Chase Manhattan Bank, as trustee, that are described in the
Registration Statement (together, the "NiSource Indenture") have been duly
executed and delivered; (ii) the merger of Company Acquisition Corp. into
Columbia has been consummated pursuant to the alternative structure described in
Section 2.4 of the Merger Agreement; and (iii) the NiSource Debt Securities have
been duly executed and authenticated in accordance with the NiSource Indenture.

                  10. The NiSource Share Purchase Units will be valid and
legally binding obligations of New NiSource, subject to bankruptcy, insolvency,
fraudulent transfer, reorganization, moratorium and similar laws of general
applicability relating to or affecting creditors' rights and to general equity
principles, at such time as the conditions set forth in paragraphs 7 and 9 of
this opinion have been satisfied.

                  We express opinions herein with respect to the applicability
of the Delaware General Corporation Law, the Indiana Business Corporation Law,
the laws of the State of New York generally applicable to commercial and
financial matters and the United States federal laws, and we express no opinion
as to any other laws or the laws of any other jurisdiction.

                  We hereby consent to the filing of this opinion as Exhibit 5.1
to the Registration Statement and to the reference to us under the caption
"Legal Matters" in the Joint Proxy Statement/Prospectus contained in the
Registration Statement.



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NiSource, Inc. and New NiSource Inc.
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                                       Very truly yours,

                                       SCHIFF HARDIN & WAITE


                                       By: /s/ Frederick L. Hartmann
                                          --------------------------------------
                                          Frederick L. Hartmann

FLH/