[LETTERHEAD OF WEIL, GOTSHAL & MANGES LLP]
 
                               NOVEMBER 21, 1996
 
MILLENNIUM AMERICA INC.
MILLENNIUM CHEMICALS INC.
99 WOOD AVENUE SOUTH
ISELIN, NEW JERSEY 08830
 
         RE: MILLENNIUM AMERICA INC. AND MILLENNIUM
             CHEMICALS INC. REGISTRATION STATEMENT ON
             FORM S-1 (REGISTRATION NOS. 333-15975 AND 333-15975-01)
 
Ladies and Gentlemen:
 
     We have acted as counsel to Millennium America Inc., a Delaware corporation
('Millennium  America'), and  Millennium Chemicals Inc.,  a Delaware corporation
('Millennium'),  in  connection  with  the  preparation  and  filing  with   the
Securities   and  Exchange  Commission  (the  'Commission')  of  a  Registration
Statement on  Form  S-1  (Registration  Nos.  333-15975  and  333-15975-01)  (as
amended,  the 'Registration  Statement') under  the Securities  Act of  1933, as
amended (the 'Securities Act'),  and will act as  counsel to Millennium  America
and  Millennium in connection with any future Registration Statement on Form S-1
which may  be  filed with  the  Commission pursuant  to  Rule 462(b)  under  the
Securities  Act (a  '462(b) Registration Statement'),  with respect  to (i) debt
securities to be issued by Millennium  America in an aggregate principal  amount
of  $750,000,000 or  such other amount  as may  be set forth  in a pre-effective
amendment to the Registration Statement and any additional securities which  may
be   registered  pursuant  to   Rule  462(b)  under   the  Securities  Act  (the
'Securities') and (ii) guarantees to be endorsed on the Securities by Millennium
(the 'Guarantees'). The Securities  will be issued, and  the Guarantees will  be
endorsed  on  the  Securities,  pursuant  to  the  terms  of  an  Indenture (the
'Indenture'), to be entered  into among Millennium  America, Millennium and  The
Bank  of  New York,  as trustee  (the 'Trustee'),  filed as  Exhibit 4.1  to the
Registration Statement.




MILLENNIUM AMERICA INC.
MILLENNIUM CHEMICALS INC.
NOVEMBER 21, 1996
PAGE ?
 
     In so acting, we have examined originals or copies, certified or  otherwise
identified  to our satisfaction,  of the Registration  Statement, the Indenture,
the forms of Note  and Debenture included in  the Indenture, and such  corporate
records,  agreements, documents and other  instruments, and such certificates or
comparable documents of public officials and of officers and representatives  of
Millennium America and Millennium, and have made such inquiries of such officers
and representatives, as we have deemed relevant and necessary as a basis for the
opinions hereinafter set forth.
 
     In such examination, we have assumed the genuineness of all signatures, the
authenticity  of all documents  submitted to us as  originals, the conformity to
original documents  of documents  submitted to  us as  certified or  photostatic
copies and the authenticity of the originals of such latter documents. As to all
questions  of fact  material to  this opinion  that have  not been independently
established, we  have  relied  upon  certificates  or  comparable  documents  of
officers and representatives of Millennium America and Millennium.
 
     Based on the foregoing, and subject to the qualifications stated herein, we
are of the opinion that:
 
          1.  The Securities  are duly  authorized and,  when duly  executed and
     delivered by Millennium America, authenticated by the Trustee in accordance
     with the  terms of  the Indenture,  and sold  and delivered  by  Millennium
     America  as  contemplated  by  the Registration  Statement  and  any 462(b)
     Registration Statement,  and  paid  for by  the  purchasers  thereof,  will
     constitute  the legal, valid and binding obligations of Millennium America,
     enforceable  against  it  in  accordance  with  their  terms,  subject   to
     applicable  bankruptcy, insolvency,  fraudulent conveyance, reorganization,
     moratorium and  similar  laws  affecting  creditors'  rights  and  remedies
     generally,  and  subject, as  to enforceability,  to general  principles of
     equity, including principles of  commercial reasonableness, good faith  and
     fair  dealing (regardless of whether enforcement  is sought in a proceeding
     at law or in equity).
 
          2. The  Guarantees  are duly  authorized  and, when  endorsed  on  the
     Securities   by  Millennium  and  sold   and  delivered  by  Millennium  as
     contemplated by  the Registration  Statement  and any  462(b)  Registration
     Statement,  will  constitute the  legal, valid  and binding  obligations of
     Millennium, enforceable against it in



MILLENNIUM AMERICA INC.
MILLENNIUM CHEMICALS INC.
NOVEMBER 21, 1996
PAGE ?
 
accordance with  their  terms,  subject to  applicable  bankruptcy,  insolvency,
fraudulent  conveyance,  reorganization, moratorium  and similar  laws affecting
creditors' rights and remedies generally, and subject, as to enforceability,  to
general principles of equity, including principles of commercial reasonableness,
good  faith and fair dealing  (regardless of whether enforcement  is sought in a
proceeding at law or in equity).
 
     The opinions expressed herein are limited to  the laws of the State of  New
York,  the corporate laws of  the State of Delaware and  the federal laws of the
United States, and we express no opinion as to the effect on the matters covered
by this letter of the laws of any other jurisdiction.
 
     The opinions  expressed herein  are  rendered solely  for your  benefit  in
connection wit the transactions described herein. Those opinions may not be used
or relied upon by any other person, nor may this letter or any copies thereof be
furnished  to a third party, quoted, cited  or otherwise referred to without our
prior written consent, except that we hereby consent to the use of this  opinion
as  an exhibit to  (i) the Registration Statement,  (ii) any 462(b) Registration
Statement which may  be filed by  Millennium America and  Millennium, and  (iii)
applications  to the  securities commissioners of  various states  of the United
States for registration or  qualification of the  Securities and the  Guarantees
under the securities laws of such states. We further consent to the reference to
our  firm under the caption 'Legal Matters' in the Prospectus which is a part of
the Registration Statement or any 462(b) Registration Statement.
 
                                          Very truly yours,
 
                                          /s/ Weil, Gotshal & Manges LLP