<PAGE>

                                                                     EXHIBIT 4.6

Unofficial English Translation of:
Register of Notarial Instr., Rec. No. 2002/___
May 20, 2002
Stephan Cueni, Notary Public
Basel, Switzerland


                                     E.ON AG

                                     RAG AG

                              RAG BETEILIGUNGS-GMBH

                             EBV AKTIENGESELLSCHAFT


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

                           RUHRGAS PURCHASE AGREEMENT

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


<PAGE>


Register of Notarial Instr., Rec. No. 2002/___


                              NOTARIZED INSTRUMENT



                                    AGREEMENT


Heard in Basel, Switzerland, this day, May 20, 2002 (May the twentieth,
two-thousand-and-two).

The persons below appeared before me, the undersigned Notary Public,

                                 STEPHAN CUENI,

at my chambers in Basel, Switzerland:

1.      Mr. Johannes Perlitt, born August 29, 1962, Attorney-at-Law, German
        citizen, having his principal place of business at Mainzer Landstrasse
        46, D-60325 Frankfurt am Main, Germany, and residing
        at____________________________________________________, and identified
        to the undersigned Notary Public by means of a valid national identity
        card, and

        according to his own declaration, acting not on his own behalf, but
        rather, with all personal liability excluded, as the duly authorized
        representative of

        RAG Aktiengesellschaft, having its registered office at Rellinghauser
        Strasse 1-11, D-45128 Essen, Germany, and being registered under
        Registration No. HRB 1712 in the Commercial Register of the District
        Court (Amtsgericht), Essen, Germany,

        as evidenced by a power of attorney dated May 16, 2002, the original of
        which was submitted to the undersigned Notary Public, and of which a
        copy, duly authorized by the undersigned Notary Public, is annexed
        hereto, said power of attorney being supported by an attested specimen
        of the holder's signature and a notarized instrument certifying the
        holder as a duly authorized representative,


                                      - hereinafter also referred to as "RAG" -;

<PAGE>
                                                                               2

2.      Ms. Barbara Zihlmann (lic.iur.), born February 20, 1975, lawyer, Swiss
        citizen, residing at Schulgasse 12, CH-4105 Biel-Benken, Switzerland, of
        identity established to the satisfaction of the undersigned Notary
        Public, and

        according to her own declaration, acting not on her own behalf, but
        rather, with all personal liability excluded, as the duly authorized
        representative of

        RAG Beteiligungs-GmbH, having its registered office at Rellinghauser
        Strasse 1-11, D-45128 Essen, Germany, and being registered under
        Registration No. HRB 5398 in the Commercial Register of the District
        Court (Amtsgericht), Essen, Germany,

        as evidenced by a power of attorney dated May 16, 2002, the original of
        which was submitted to the undersigned Notary Public, and of which a
        copy, duly authorized by the undersigned Notary Public, is annexed
        hereto, said power of attorney being supported by an attested specimen
        of the holder's signature and a notarized instrument certifying the
        holder as a duly authorized representative,

                                       - hereinafter also referred to as "BG" -;

3.      Mr. Philipp Rupp (lic.iur.), born June 10, 1970, lawyer, Swiss citizen,
        residing at Rebgasse 21, CH-4058 Basel, Switzerland, of identity
        established to the satisfaction of the undersigned Notary Public, and

        according to his own declaration, acting not on his own behalf, but
        rather, with all personal liability excluded, as the duly authorized
        representative of

        EBV Aktiengesellschaft, having its registered office in D-52134
        Herzogenrath, Germany, and being registered under Registration No. HRB
        293 in the Commercial Register of the District Court (Amtsgericht), at
        Aachen, Germany,

        as evidenced by a power of attorney dated _____________, the original of
        which was submitted to the undersigned Notary Public, and of which a
        copy, duly authorized by the undersigned Notary Public, is annexed
        hereto, said power of attorney being supported by an attested specimen
        of the holder's signature and a notarized instrument certifying the
        holder as a duly authorized representative,


                                      - hereinafter also referred to as "EBV" -;


                Register of Notarial Instr., Rec. No. 2002/____Cu

<PAGE>
                                                                               3

4.      Dr. Olaf Muller-Michaels, born January 27, 1967, Attorney-at-Law, German
        citizen, having his principal place of business at Breite Strasse 69,
        D-40213 Dusseldorf, Germany, and residing at Kleverstrasse 73, D-40477
        Dusseldorf, Germany, and identified to the undersigned Notary Public by
        means of a valid national identity card, and,

        according to his own declaration, acting not on his own behalf, but
        rather, with all personal liability excluded, as the duly authorized
        representative of

        E.ON AG, a stock corporation having its registered office at E.ON-Platz
        1, D-40479 Dusseldorf, Germany, and being registered under Registration
        No. HRB 22315 in the Commercial Register of the District Court
        (Amtsgericht), Dusseldorf, Germany,

        as evidenced by a power of attorney dated May 17, 2002, the original of
        which was submitted to the undersigned Notary Public, and of which a
        copy, duly authorized by the undersigned Notary Public, is annexed
        hereto, said power of attorney being supported by an attested specimen
        of the holder's signature and a notarized instrument certifying the
        holder as a duly authorized representative,

                                     - hereinafter also referred to as "E.ON" -.


  - Hereinafter, RAG, BG, EBV and E.ON are also referred to collectively as "the
                                                                     Parties" -.


The Notary Public explained to the persons appearing the prohibition on
conflicts of interest imposed on Notaries Public by the Notaries Public
legislation of the City of Basel (EG ZGB Section 233(1)(4)) and by the German
Notarization and Authentication Act (Beurkundungsgesetz, Section 3(1)(7)).
Accordingly, the Parties and the Notary Public confirmed that neither the Notary
Public, his practice partners, nor any person with whom the Notary public works
in a professional capacity or with whom the Notary Public shares chambers within
the meaning of said legislation had had any prior dealings with the matter
herein notarized. The persons appearing, acting in the capacities as defined
herein above, made the following declarations and requested that said
declarations be notarized and entered in the Register of Notarial Instruments:



                Register of Notarial Instr., Rec. No. 2002/____Cu

<PAGE>
                                                                               4

                                    Recital:


A.      RAG holds a stake in Ruhrgas AG, Essen, ("Ruhrgas") equivalent to
        approximately 18.3949% ("stake in Ruhrgas"), made up as follows:

         -      a direct interest of approximately 0.1480 %; that is, of the
                Euro 1,125,000,000 capital stock in Ruhrgas, which is divided
                into 440,000,000 non-certificated quasi no-par-value shares
                (Stuckaktien), RAG directly owns 651,200 shares ("Ruhrgas
                shares"),

         -      an indirect interest equivalent to approximately 18.0377432 %
                (the equivalent of a Euro 202,924,611 stake in the capital
                stock of Ruhrgas) via its subsidiary, BG, which holds a stake
                with a nominal value of Euro 83,002,970.61 ("eighty-three
                million, two-thousand, nine-hundred-and-seventy euro and
                sixty-one euro cents") in Bergemann GmbH, Essen,
                ("Bergemann"), a company registered under Registration No. HRB
                5963 in the Commercial Register held at the District Court,
                Essen, and which in turn holds a stake in Ruhrgas equal to
                approximately 34.7558 %, and

         -      an indirect interest equivalent to approximately
                0.20920906666667 % (the equivalent of a Euro 2,353,602 stake
                in the capital stock of Ruhrgas) via EBV, an affiliate in
                which RAG indirectly holds approximately 99% of the stock,
                which holds a stake with a nominal value of Euro 962,711.48
                ("nine-hundred-and-sixty-two thousand seven-hundred-and-eleven
                euro and forty-eight euro cents") in Bergemann (the stakes in
                Bergemann held by BG and EBV will, in the following, be
                referred to collectively as "RAG's holdings in Bergemann").

B.      Bergemann's company Bylaws (hereinafter also referred to as
        "Bergemann's Bylaws") provides that any shareholder wishing to
        sell its shares in Bergemann must first offer the same for sale to the
        other shareholders (hereinafter this right of the other shareholders to
        be offered shares for sale will also be referred to as the "right of
        first option"). The shareholders in Bergemann are the Parties and the
        following:

        -       Vodafone Aktiengesellschaft, Dusseldorf, Germany

        -       Thyssen Krupp AG, Essen and Duisburg, Germany



                Register of Notarial Instr., Rec. No. 2002/____Cu
<PAGE>
                                                                               5

        -       RWE-DEA Aktiengesellschaft fur Mineraloel und Chemie, Hamburg,
                Germany

        -       Gelsenberg Aktiengesellschaft, Hamburg, Germany

        -       Harpen Aktiengesellschaft, Dortmund, Germany

        -       Hydro Gas and Chemicals GmbH, Bad Honningen, Germany

        -       RWE Systems AG, Essen, Germany

        -       Preussag Energie GmbH, Lingen (Ems), Germany

        For various reasons, most notably the agreements reached by E.ON and
        Bergemann's shareholders, the Parties are proceeding on the basis that
        the Bergemann shareholders will not make use of their rights of first
        option.

C.      Under the Investor Rights Agreements between the Ruhrgas shareholders
        and the Ruhrgas company dated January 9, 1966 and March 28, 1968
        (hereinafter also referred to collectively as the "Investor Rights
        Agreements"), shareholders wishing to sell Ruhrgas shares are required
        to offer those shares for sale to the other shareholders first; however,
        this obligation does not apply to transfers of Ruhrgas shares between
        existing shareholders, as is the case here. Apart from this, Section 3
        of the Ruhrgas company Bylaws states that any transfer of Ruhrgas
        shares requires the approval of the Ruhrgas shareholders at a general
        meeting (Hauptversammlung).

D.      RAG is willing to sell its stake in Ruhrgas, and E.ON is willing to
        acquire this stake. To this end, E.ON and RAG on March 1 and March 5,
        2003, signed a Heads of Agreement for the sale and purchase of RAG's
        stake in Ruhrgas ("Heads of Agreement"). In the Heads of Agreement, E.ON
        and RAG agreed that RAG would sell its stake in Ruhrgas only if RAG, by
        using the purchase money from the sale of the stake in Ruhrgas as well
        as other sources of finance, were able to acquire and finance a majority
        holding in another company that, from RAG's viewpoint, is suitable and
        comparable to the stake in Ruhrgas.

E.      RAG, BG, BG's wholly-owned subsidiary RAG Projektgesellschaft mbH ("the
        Offerer"), EBV, E.ON, and E.ON's wholly-owned subsidiaries Chemie
        Verwaltungs AG ("CVAG") and E.ON Vermogensanlage GmbH ("E.ON VG") have
        on this day in the presence of the authenticating Notary Public entered
        into a "Framework Agreement"


                Register of Notarial Instr., Rec. No. 2002/____Cu
<PAGE>
                                                                               6

        (Register of Notarial Instr., Rec. No 2002/213), to which the present
        agreement refers. The Framework Agreement provides for the conclusion of
        the present agreement (the "Ruhrgas Purchase Agreement") and bundles the
        same with various other transactions.

NOW, THEREFORE, in consideration of the above provisions, the Parties hereby
agree as follows:


                         I. RAG'S HOLDINGS IN BERGEMANN

1.      Acquisition of RAG's holdings in Bergemann

1.1     BG and EBV hereby offer RAG's holdings in Bergemann for sale to E.ON,
        and E.ON accepts this offer. BG and EBV hereby transfer RAG's holdings
        in Bergemann to E.ON, and E.ON accepts this transfer, provided, however,
        that the transfer shall not take effect unless and until the conditions
        precedent described in clause 2 hereof have been met and unless and
        until the acquisition price and the finalized or provisional increase
        amount (as the case may be) for RAG's holdings in Bergemann plus
        interest ("completion of the sale of RAG's holdings in Bergemann") as
        described in clauses 1.2 and 1.4 hereof have been paid.

1.2     The price for RAG's holdings in Bergemann is Euro 1,894,733,848
        (one-billion eight-hundred-and-ninety-four million
        seven-hundred-and-thirty-three-thousand eight-hundred-and-forty-eight
        euro, which hereinafter will also be referred to as the "acquisition
        price for RAG's holdings in Bergemann"). The acquisition price for RAG's
        holdings in Bergemann shall be increased by the amount of money that
        would be allotted to RAG's holdings in Bergemann if Bergemann's entire
        net income for the 2001 financial year were distributed to its
        shareholders, provided, however, the amount of this increase
        (hereinafter also referred to as the "Increase Amount") shall not be
        less than Euro 78,018,453 (seventy-eight million eighteen-thousand
        four-hundred-and-fifty-three euro). The acquisition price for RAG's
        holdings in Bergemann including the Increase Amount will hereinafter
        also be referred to as the "purchase price for RAG's holdings in
        Bergemann." The purchase price for RAG's holdings in Bergemann shall
        bear interest at the rate of 4% per


                Register of Notarial Instr., Rec. No. 2002/____Cu
<PAGE>
                                                                               7

        annum (30/360 day-count) as from January 1, 2002. The purchase price for
        RAG's holdings in Bergemann plus interest thereon shall be allotted
        between BG and EBV pro rata the nominal values of their respective
        holdings in Bergemann.

1.3     The sale of RAG's holdings in Bergemann shall take commercial effect at
        midnight (00:00) on January 1, 2002 (hereinafter also referred to as the
        "Effective Date"). From the Effective Date forward, E.ON shall be
        entitled to all such rights to share in Bergemann's profits as attach to
        RAG's holdings in Bergemann. All dividend payments that are allotted to
        RAG's holdings in Bergemann after the conclusion of this Ruhrgas
        Purchase Agreement but prior to the date when the transfer to E.ON of
        RAG's holdings in Bergemann becomes effective shall have the effect of
        reducing the interest-inclusive purchase price for RAG's holdings in
        Bergemann by the amount of said dividend payments.

1.4     The purchase price for RAG's holdings in Bergemann together with
        interest thereon shall be due five bank working days after all the
        conditions precedent, as described in clause 2 hereof, for the transfer
        of RAG's holdings have been met (hereinafter this due date for payment
        is also referred to as the "Closing"). If, at the time of Closing, the
        Increase Amount has not yet been finalized, then the price due shall be
        the acquisition price plus a preliminary increase amount of Euro
        78,018,543 plus interest thereon as per clause 1.2 hereof.

1.5     That portion of the interest-inclusive purchase price for RAG's holdings
        in Bergemann which is payable to EBV shall be remitted to a bank account
        which EBV shall designate in writing sufficiently in advance of Closing.
        Similarly, that portion of the interest-inclusive purchase price for
        RAG's holdings in Bergemann which is payable to BG shall be remitted to
        a bank account which BG shall designate in writing sufficiently in
        advance of Closing. Pursuant to clause 15.1 of the Framework Agreement,
        BG is entitled to transfer and pledge to the Settlement Bank (as defined
        in the Framework Agreement) its share of the interest-inclusive purchase
        price for RAG's holdings in Bergemann.

1.6     E.ON shall neither by right of retention withhold payment of the
        interest-inclusive purchase price for RAG's holdings in Bergemann, nor
        offset the same against any claim unless the claim forming the basis of
        the right of retention or offsetting is a finally and unappealably
        proven E.ON claim against BG.


                Register of Notarial Instr., Rec. No. 2002/____Cu
<PAGE>
                                                                               8

1.7     If E.ON fails to pay on the due date, then the interest-inclusive
        purchase price for RAG's holdings in Bergemann shall as from the due
        date attract penalty interest at a rate equal to the EURIBOR three-month
        rate for the due date plus 2.5% p.a.

2.      Conditions precedent and Closing

2.1     The transfer of RAG's holdings in Bergemann shall not take effect unless
        and until:

2.1.1   in response to its applications, dated February 18 and March 5, 2002,
        for ministerial approval, pursuant to Section 42 of the German Antitrust
        Act (GWB), for the merger proposals (as per the Gelsenberg notification
        dated August 15, 2001 and the Bergemann notification dated November 9,
        2001) that were vetoed by the German Federal Cartel Office, E.ON has
        been granted ministerial approval that is either unconditional or that
        is subject only to conditions of such a nature that E.ON has been able
        to communicate its agreement thereto in writing to RAG within four weeks
        after the special ministerial approval was granted,

        and either

        as of the time when all the other conditions precedent are met, no
        competent court has issued any ruling overturning or barring either the
        ministerial approval or its enforcement,

        or,

        approval has been obtained for the above-stated merger proposals by
        means of appeal proceedings, providing that the approval so obtained is
        enforceable; and

2.1.2   each of the other shareholders in Bergemann has expressly waived its
        right of first option or, in response to the offer for the sale of RAG's
        holdings in Bergemann made by BG and EBV to their co-shareholders in
        Bergemann as per clause 5.1 hereof, has, in accordance with Section
        21(1) of Bergemann's Bylaws, given written notice that it does not
        intend to take up said offer, or, while wishing to take up said offer
        has nonetheless not within two months reached agreement with BG and EBV
        as to the purchase price for the holdings offered, and has not, within
        three months of receipt of the offer by Bergemann, demanded that the
        purchase price for the holdings offered be determined by an arbitrator's
        opinion; and

                Register of Notarial Instr., Rec. No. 2002/____Cu
<PAGE>
                                                                               9

2.1.3   either the EU Commission and the competent antitrust authorities in the
        USA and Canada have expressly given their permission for the acquisition
        of the stake in Degussa and the Shareholders' Agreement (as defined in
        the Framework Agreement) with E.ON to proceed, or all applicable
        deadline periods for the imposition of prohibitions by the EU Commission
        and the aforementioned antitrust authorities have elapsed without any
        prohibitions being imposed on the above-stated transactions; and

2.1.4   the government of the Federal Republic of Germany and the government of
        the federal state (Land) of North Rhine-Westphalia have unconditionally
        approved both the RAG Projektgesellschaft mbH's Tender Offer for Degussa
        AG and the Ruhrgas Purchase Agreement.

2.2     As regards the condition precedent stated in clause 2.1.4 hereof, BG has
        the right (but not the obligation) at any time to unilaterally waive the
        requirement that the government approvals be unconditional.

2.3     Closing in the sense intended by this Ruhrgas Purchase Agreement shall
        take place five bank working days after the last of the conditions
        precedent has been met.

2.4     The condition precedent specified in clause 2.1.3 hereof must be met by
        March 31, 2003 at the very latest, and the other conditions precedent by
        January 31, 2003 at the very latest, otherwise the sale of the stake in
        Ruhrgas shall be deemed to have irrevocably failed.

3.      Purchase price adjustment

        If the finalized Increase Amount should turn out to be greater than the
        preliminary increase amount paid at the time of Closing, then E.ON shall
        remit the difference to the accounts defined in clause 1.5 hereof within
        10 (ten) working days following finalization of the Increase Amount.

4.      Warranty

        Subject to the exclusion of all warranty claims provided by statute, BG
        and EBV hereby warrant and represent that those of RAG's holdings in
        Bergemann that each of them sells to E.ON are fully paid-up, are their
        property, and, except for the rights detailed in the Investor Rights
        Agreements and Bergemann's Bylaws, are not


                Register of Notarial Instr., Rec. No. 2002/____Cu
<PAGE>
                                                                              10

        encumbered by third-party rights. BG and EBV give no other warranties
        and make no other representations.

5.      Rights of first option

5.1     RAG and BG have by declaration to Bergemann on this day offered RAG's
        stakes in Bergemann for sale to their fellow Bergemann shareholders as
        required by Section 21(1) of Bergemann's Bylaws.

5.2     E.ON intends to acquire all the shares in Bergemann. To this end, the
        Parties shall exercise their best endeavors to avoid delays in the
        process of acquisition by E.ON, to expedite the first-option process
        mandated by Bergemann's Bylaws, and to ensure that all Bergemann
        shareholders refrain from exercising the rights of first option accorded
        them by Bergemann's Bylaws.

5.3     E.ON hereby irrevocably waives its right to require that the purchase
        price for RAG's holdings in Bergemann be determined in accordance with
        Section 22(2) of Bergemann's Bylaws by an arbitrator's opinion. E.ON, BG
        and EBV shall to the extent permitted by law use their influence in such
        a way that the other Bergemann shareholders likewise refrain from
        insisting that the purchase price be determined by an arbitrator's
        opinion in accordance with Section 22(2) of Bergemann's Bylaws.

5.4     If a Bergemann shareholder nonetheless insists that the purchase price
        be determined by an arbitrator's opinion in accordance with Section
        22(2) of Bergemann's Bylaws, then the purchase price agreed upon in this
        Ruhrgas Purchase Agreement shall nonetheless remain binding as between
        E.ON for one part, and BG and EBV for the other.

5.5     BG and EBV hereby irrevocably undertake and agree to waive any and all
        first-option duties they may be owed and any and all rights of first
        option they may have on the basis of Bergemann's Bylaws and the Investor
        Rights Agreements.


                Register of Notarial Instr., Rec. No. 2002/____Cu
<PAGE>
                                                                              11

                               II. RUHRGAS SHARES


6.      Acquisition of the Ruhrgas shares

6.1     RAG hereby offers the 651,200 quasi no-par-value shares (Stuckaktien) it
        holds in Ruhrgas for sale to E.ON, and E.ON accepts this offer. RAG
        hereby transfers the 651,200 quasi no-par-value shares (Stuckaktien) it
        holds in Ruhrgas to E.ON, and E.ON accepts this transfer, provided,
        however, that the transfer shall not take effect unless and until (i)
        all the conditions precedent defined in clause 2 hereof have been met,
        (ii) the acquisition price and the finalized or provisional increase
        amount (as the case may be) for the Ruhrgas shares plus interest as
        described in clauses 6.3 and 6.5 hereof have been paid, (iii) the
        acquisition price and the finalized or provisional increase amount (as
        the case may be) for RAG's holdings in Bergemann plus interest as
        described in clauses 1.2 and 1.4 hereof have been paid, and (iv) the
        share transfer has been approved in accordance with clause 8 hereof by
        Ruhrgas via a general meeting of its shareholders.

6.2     If requested by E.ON, RAG shall at the time of Closing, as defined in
        clause 6.5 hereof, give all such further declarations and perform all
        such further measures as may still be necessary as a result of and in
        relation to the transfer of property in the Ruhrgas shares to E.ON.

6.3     The total price for the Ruhrgas shares is Euro 15,368,095
        (fifteen-million three-hundred-and-sixty-eight-thousand and ninety-five
        euro, hereinafter also referred to as the "acquisition price for the
        Ruhrgas shares"). The acquisition price for the Ruhrgas shares shall be
        increased by the amount of money that would be allotted to Ruhrgas
        shares sold pursuant to clause 6.1 hereof if Ruhrgas' entire net income
        for the 2001 financial year were distributed to its shareholders,
        provided, however, that the amount of this increase (hereinafter also
        referred to as the "Increase Amount for the Ruhrgas shares") shall not
        be less than Euro 632,804 (six-hundred-and-thirty-two-thousand
        eight-hundred-and-four euro). The acquisition price for the Ruhrgas
        shares including the Increase Amount for the Ruhrgas shares will
        hereinafter also be referred to as the "purchase price for the Ruhrgas
        shares." The purchase price for the Ruhrgas shares shall bear interest
        at the rate of 4% per annum (30/360 day-count) as from January 1, 2002.


                Register of Notarial Instr., Rec. No. 2002/____Cu
<PAGE>
                                                                              12

6.4     The purchase price for the Ruhrgas shares includes full and final
        payment for all rights to share in the profits of Ruhrgas. Any dividend
        payments that Ruhrgas may make to RAG after this Ruhrgas Purchase
        Agreement is concluded but before the transfer of the Ruhrgas shares to
        E.ON takes effect shall have the effect of reducing the
        interest-inclusive purchase price for the Ruhrgas shares by the amount
        of said dividend payments.


6.5     The purchase price for the Ruhrgas shares together with interest thereon
        shall be due five bank working days after all the conditions precedent,
        as described in clause 2 hereof, have been met and after Ruhrgas has by
        general meeting of its shareholders approved the share transfer pursuant
        to clause 8 hereof (hereinafter this due date for payment is also
        referred to as the "Closing for the Ruhrgas shares"). If, at the time of
        Closing for the Ruhrgas shares, the Increase Amount for the Ruhrgas
        shares has not yet been finalized, then the price due shall be the
        acquisition price for the Ruhrgas shares plus a preliminary increase
        amount of Euro 632,804 plus interest thereon as per clause 6.3 hereof.

6.6     If the finalized Increase Amount for the Ruhrgas shares should turn out
        to be greater than the preliminary increase amount paid at the time of
        Closing for the Ruhrgas shares, then E.ON shall pay the difference
        within 10 (ten) working days following finalization of the Increase
        Amount for the Ruhrgas shares.

6.7     E.ON shall remit the interest-inclusive purchase price for the
        Ruhrgas shares to a bank account which RAG shall nominate in writing
        sufficiently in advance of Closing for the Ruhrgas shares.

6.8     E.ON shall neither by right of retention withhold payment of the
        interest-inclusive purchase price for the Ruhrgas shares, nor offset the
        same against any claim unless the claim forming the basis of the right
        of retention or offsetting is a finally and unappealably proven E.ON
        claim against RAG.

6.9     If E.ON fails to pay on the due date, then the interest-inclusive
        purchase price for the Ruhrgas shares shall as from the due date attract
        penalty interest at a rate equal to the EURIBOR three-month rate for the
        due date plus 2.5% p.a.


                Register of Notarial Instr., Rec. No. 2002/____Cu
<PAGE>
                                                                              13

7.      Warranty

        Subject to the exclusion of all warranty claims provided by statute, RAG
        hereby warrants and represents that the Ruhrgas shares it sells to E.ON
        are fully paid-up, are RAG's property, and, except for the rights
        described in Ruhrgas' Bylaws, are not encumbered by third-party rights.
        RAG gives no other warranties and makes no other representations.

8.      Share transfer subject to Ruhrgas consent

8.1     The Parties agree and accept that the share transfer forming the subject
        of this Ruhrgas Purchase Agreement requires the prior approval of
        Ruhrgas via a general meeting of its shareholders. The Parties further
        agree that the seeking of Ruhrgas approval is subject to E.ON consent.
        The Parties shall in their capacities as direct and indirect
        shareholders in Ruhrgas endeavor to secure Ruhrgas approval for the
        share transfer.

8.2     RAG hereby gives an irrevocable undertaking to refrain from exercising
        the right of first option (to be offered shares for sale) that accrues
        to RAG pursuant to the Investor Rights Agreements whenever other parties
        to said Investor Rights Agreements intends to sell Ruhrgas shares.

8.3     If Ruhrgas via a general meeting of its shareholders fails to give its
        approval for the share transfer on or before January 31, 2003, then the
        following provisions shall apply in lieu of the share purchase
        agreement:

8.3.1   The offer for sale of RAG's holdings in Bergemann and completion of said
        sale provided for by Part I of this Ruhrgas Purchase Agreement shall be
        unaffected.

8.3.2   RAG shall have the right, valid for a period of ten years as from the
        conclusion of this Ruhrgas Purchase Agreement, to offer for sale to E.ON
        the 651,200 Ruhrgas shares RAG holds for a price of Euro 15,368,095
        (fifteen-million three-hundred-and-sixty-eight-thousand and ninety-five
        euro) plus interest at the rate of 4% per annum (30/360 day-count)
        calculated as from the start of the financial year in which the transfer
        of the shares takes place. In addition, RAG shall be entitled to any
        Ruhrgas dividends for the preceding Ruhrgas financial year, provided
        that said dividends are paid out of the net profit for said preceding
        financial year. If necessary, the dividends


                Register of Notarial Instr., Rec. No. 2002/____Cu
<PAGE>
                                                                              14


        for the financial year preceding the year of the transfer shall be paid
        by way of an increase in the purchase price.

8.3.3   For a validity period of ten years from the conclusion of this Ruhrgas
        Purchase Agreement E.ON shall have a right of first option to buy RAG's
        shares in Ruhrgas, said right ranking behind any such third-party rights
        of first option as already exist at the time when this Ruhrgas Purchase
        Agreement is concluded, as prescribed by the relevant statutes. E.ON
        shall be required to exercise its right of first option before the
        expiry of a period of two months from the time when RAG gives notice
        offering the shares for sale to E.ON.



                               III. MISCELLANEOUS



9.      Rescission

9.1     Each of the Parties shall have the right to rescind this Ruhrgas
        Purchase Agreement if the preconditions for completion of the sale of
        RAG's holdings in Bergemann, as defined in clause 2.1 hereof, are not
        met by January 31, 2003 at the latest (notwithstanding the deadline
        provisions, defined in clause 2.4, for the precondition in clause
        2.1.3). In particular, they shall have this right of rescission if the
        sale of RAG's holdings in Bergemann to E.ON is prevented by the other
        Bergemann shareholders' rights of first option.

9.2     BG and EBV must act in concert and jointly as one party when exercising
        the right of rescission and any other statutory or contractual rights of
        rescission they may have. To this end, BG and EBV hereby grant each
        other an irrevocable power of attorney to act on each other's behalf if
        and when giving notice of rescission; notice of rescission issued by one
        of these two parties will automatically extend to and bind the other.

9.3     If this Ruhrgas Purchase Agreement is rescinded, then, notwithstanding
        anything in clauses 8.3, 11, 12, and 13 hereof, none of the Parties to
        this agreement shall have any claims against any of the other Parties.


                Register of Notarial Instr., Rec. No. 2002/____Cu
<PAGE>
                                                                              15

10.     RAG's duty to ensure performance by BG and EBV

        RAG shall ensure that BG and EBV perform their obligations under this
        Ruhrgas Purchase Agreement.

11.     Costs

        E.ON and BG shall each pay half the costs of notarizing and performing
        this Ruhrgas Purchase Agreement. Each party shall pay the costs of their
        own consultants and advisors.

12.     Arbitration clause

        All disputes arising out of or in connection with this contract or
        relating to its validity shall be settled in accordance with the Rules
        of Arbitration of the German Institution of Arbitration (DIS), Such
        settlement shall be final, binding and without recourse to the ordinary
        courts of law. The venue for arbitration proceedings is Dusseldorf,
        Germany. Each dispute shall be heard by a panel of three arbitrators. If
        the Parties are unable to agree on the appointment of the presiding
        arbitrator, the presiding arbitrator shall be appointed by the President
        of the Upper Regional Court (OLG), Dusseldorf.

13.     Final provisions

13.1    This agreement supersedes and replaces all prior oral or written
        agreements between the Parties that deal with the subject matter of this
        agreement; the Heads of Agreement is the sole exception to this. There
        are no collateral agreements.

13.2    Any additions and amendments to this agreement must be in writing unless
        notarization is required. The same applies to any changes to this
        clause.

13.3    If any provision of this agreement should be or becomes invalid or
        unenforceable, whether wholly or in part, then that provision shall be
        severed, and the remaining provisions of the this agreement shall remain
        valid and enforceable. The same shall apply if this agreement is found
        to contain a gap or gaps. The Parties shall cure the invalid or
        unenforceable provision or gap by substituting a valid and enforceable
        provision which as nearly as permissible by law approximates that which
        the Parties intended or, judging by the spirit and intent of the
        Framework Agreement, would have intended if they had considered the
        point at issue when entering into the Framework


                Register of Notarial Instr., Rec. No. 2002/____Cu
<PAGE>
                                                                              16


        Agreement or, subsequently thereto, when adding a provision to the
        Framework Agreement. This shall apply even if the invalidity of a
        provision relates to a scope of service or a time parameter (deadline
        period or deadline date); in such cases, the Parties shall cure the
        invalid scope of service or time parameter by substituting a valid scope
        of service or time parameter which as nearly as possible approximates
        the intended scope of service or time parameter.

13.4    If there are any conflicts between this agreement and the Framework
        Agreement, or if there are any uncertainties as to construction and
        interpretation, then the Framework Agreement shall take precedence.


                                                        (continued on next page)


                Register of Notarial Instr., Rec. No. 2002/____Cu
<PAGE>


IN WITNESS WHEREOF, I, the undersigned Notary Public, read this written record
to the persons appearing, who then indicated their approval and acceptance of
this written record by signing the same in their own hand, whereupon I signed
the same in my own hand and affixed my official seal.

Done in Basel, on this day, May 20 (twentieth), 2002 (two-thousand-and-two)



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



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



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



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



                                               --------------------------------
                                               Stephan Cueni, Notary Public


Register of Notarial Instr., Rec. No. 2002/____