Document:

EXHIBIT 10.46

                   THIRD AMENDMENT TO NOTE PURCHASE AGREEMENT

     THIS THIRD AMENDMENT,  dated as of November 22, 1999 (the "Amendment"),  to
the separate Note Purchase  Agreements,  dated as of December 28, 1995, is among
Seitel,  Inc. (the "Company") and each of the institutions  which is a signatory
to this Amendment (collectively, the "Noteholders").

                                    RECITALS:

     A. The Company and each of the  Noteholders  have  heretofore  entered into
separate Note Purchase  Agreements dated as of December 28, 1995  (collectively,
as  amended  and in  effect  immediately  prior  to the  effectiveness  of  this
Amendment,  the  "Existing  Note  Purchase  Agreement"),  pursuant  to which the
Company issued: (a) $25,000,000 aggregate principal amount of its 7.17% Series A
Senior  Notes due  December  30, 2001 (the  "Series A Notes"),  (b)  $27,500,000
aggregate  principal  amount of its 7.17% Series B Senior Notes due December 30,
2002 (the "Series B Notes"),  and (c)  $22,500,000  of its 7.48% Series C Senior
Notes due December 30, 2002 (the "Series C Notes",  and together with the Series
A Notes and the Series B Notes, the "Notes").

     B.  Capitalized  terms  used  herein  shall  have the  respective  meanings
ascribed  thereto in the Existing Note Purchase  Agreement unless herein defined
or the context shall otherwise require.

     C. The Company and the  Noteholders  now desire to amend the Existing  Note
Purchase  Agreement in the respects,  but only in the respects,  hereinafter set
forth.

     D. All requirements of law have been fully complied with and all other acts
and  things  necessary  to make  this  Amendment  a  legal,  valid  and  binding
instrument  according to its terms for the purposes  herein  expressed have been
done or performed.

     NOW,  THEREFORE,  for good  and  valuable  consideration  the  receipt  and
sufficiency of which are hereby acknowledged, the Company and the Noteholders do
hereby agree as follows:

SECTION 1. AMENDMENTS.

<PAGE>

     1.1  Amendment to Section  10.6(b)(i).  Section  10.6(b)(i) of the Existing
Note  Purchase  Agreement  is hereby  amended and  restated  in its  entirety as
follows:

          "(i)   Notwithstanding   the  provisions  of  Section   10.6(a),   the
     determination of whether a Transfer  involves a Substantial  Portion of the
     property  of the Company and the  Restricted  Subsidiaries,  as provided in
     Section 10.6(a)(iii)(A), shall be made without taking into account the same
     proportion of the book value  attributable to the property  subject to such
     Transfer as shall be equal to the proportion of the Net Asset Sale Proceeds
     Amount (the "Designated  Portion") to be applied to either (x) a prepayment
     of the Notes  pursuant to Section 8.2 of this Agreement and a prepayment of
     the New Notes  pursuant to Section 8.2 of the New Note Purchase  Agreement,
     pro rata based on the then  outstanding  principal  amount of and  required
     Make-Whole  Amount  (with  respect to the New Notes,  as defined in the New
     Note Purchase  Agreement) due with respect to the prepayment of each series
     of the  Notes  and the  New  Notes  (a  "Prepayment  Transfer")  or (y) the
     acquisition  of assets similar to the assets which were the subject of such
     Transfer (a "Reinvested  Transfer") within one hundred eighty (180) days of
     the consummation of such Transfer, as specified in an Officer's Certificate
     delivered  to  each  holder  prior  to,  or  contemporaneously   with,  the
     consummation of such Transfer."

     1.2  Amendment  to Schedule B.  Schedule B to the  Existing  Note  Purchase
Agreement  is hereby  amended to add,  in the  proper  alphabetical  order,  the
following defined terms:

          "New  Notes -- means the  Company's  7.03%  Series D Senior  Notes due
     February  15,  2004  in  the  original   aggregate   principal   amount  of
     $20,000,000,  7.28%  Series E Senior  Notes due  February  15,  2009 in the
     original  aggregate  principal  amount of  $75,000,000,  and 7.43% Series F
     Senior  Notes due February  15, 2009 in the  original  aggregate  principal
     amount of $43,000,000 issued pursuant to the New Note Purchase Agreement."

          "New  Note  Purchase  Agreement  -- means  each of the  separate  Note
     Purchase  Agreements  between  the Company  and the  purchasers  of the New
     Notes, dated February 12, 1999, as amended from time to time."

SECTION 2. REPRESENTATIONS AND WARRANTIES OF THE COMPANY.

     To induce the  Noteholders  to execute and deliver  this  Amendment  (which
representations  shall  survive  such  execution  and  delivery),   the  Company
represents and warrants to the Noteholders that:

          (a) the Company is a corporation duly organized,  validly existing and
     in good standing under the laws of the state of Delaware;

          (b) this Amendment has been duly authorized, executed and delivered by
     the  Company  and this  Amendment  constitutes  a legal,  valid and binding
     obligation, contract and agreement of the Company enforceable against it in
     accordance  with  its  terms,  except  as  enforcement  may be  limited  by
     bankruptcy,  insolvency,  reorganization,  moratorium  or  similar  laws or
     equitable principles relating to or limiting creditors' rights generally;

          (c)  the  Existing  Note  Purchase  Agreement,   as  amended  by  this
     Amendment,  constitutes the legal, valid and binding  obligation,  contract
     and agreement of the Company  enforceable against it in accordance with its
     terms,  except as  enforcement  may be limited by  bankruptcy,  insolvency,
     reorganization, moratorium or similar laws or equitable principles relating
     to or limiting creditors' rights generally;

          (d) the  execution,  delivery and  performance  by the Company of this
     Amendment (i) has been duly  authorized by all requisite  corporate  action
     and, if required,  shareholder action, (ii) does not require the consent or
     approval of any  governmental or regulatory body or agency,  and (iii) will
     not (A) violate (1) any  provision of law,  statute,  rule or regulation or
     its certificate of incorporation  or bylaws,  (2) any order of any court or
     any rule,  regulation  or order of any other agency or  government  binding
     upon it, or (3) any provision of any material indenture, agreement or other
     instrument to which it is a party or by which its  properties or assets are
     or may be bound, or (B) result in a breach of or constitute  (alone or with
     due  notice  or lapse  of time or  both) a  default  under  any  indenture,
     agreement or other  instrument  referred to in clause  (iii)(A)(3)  of this
     paragraph (d); and

          (e) as of the date hereof and after giving  effect to this  Amendment,
     no Default or Event of Default has occurred which is continuing.

SECTION 3. MISCELLANEOUS.

     3.1 This Amendment shall be construed in connection with and as part of the
Existing Note Purchase  Agreement,  and except as modified and expressly amended
by this Amendment, all terms, conditions and covenants contained in the Existing
Note  Purchase  Agreement  and the Notes are  hereby  ratified  and shall be and
remain in full force and effect.

     3.2 This  Amendment  constitutes  a contract  between  the  Company and the
Noteholders for the uses and purposes hereinabove set forth, and may be executed
in any  number  of  counterparts,  each  executed  counterpart  constituting  an
original, but all together only one agreement.

     3.3 Whenever any of the parties hereto is referred to, such reference shall
be deemed to include  the  successors  and  assigns of such  party,  and all the
promises  and  agreements  contained  in this  Amendment  by or on behalf of the
Company  and  the  Noteholders  shall  bind  and  inure  to the  benefit  of the
respective successors and assigns of such parties, whether so expressed or not.

     3.4 This Amendment  constitutes the final written  expression of all of the
terms hereof and is a complete and exclusive statement of those terms.

     3.5 This  Amendment  shall be governed by and construed in accordance  with
the internal laws of the State of New York.

     3.6 This  Amendment  shall  become  effective  at such  time as it has been
executed by the Company and the Required Holders.

            [The remainder of this page is intentionally left blank.
                         Next page is signature page.]

<PAGE>

     IN WITNESS  WHEREOF,  the parties  hereto have caused the execution of this
Amendment by duly authorized officers of each as of the date hereof.

                                       SEITEL, INC.

                                       By   /s/ Debra D. Valice
                                            ------------------------------------
                                            Debra D. Valice,
                                            Executive Vice President - Finance

Accepted and Agreed to:

[NOTEHOLDER]

By
  -------------------------------
Name:
Title:EXHIBIT 10.50

                   SECOND AMENDMENT TO NOTE PURCHASE AGREEMENT

     THIS SECOND AMENDMENT, dated as of November 22, 1999 (the "Amendment"),  to
the separate Note Purchase  Agreements,  dated as of February 12, 1999, is among
Seitel,  Inc. (the "Company") and each of the institutions  which is a signatory
to this Amendment (collectively, the "Noteholders").

                                    RECITALS:

     A. The Company and each of the  Noteholders  have  heretofore  entered into
separate Note Purchase  Agreements dated as of February 12, 1999  (collectively,
as  amended  and in  effect  immediately  prior  to the  effectiveness  of  this
Amendment,  the  "Existing  Note  Purchase  Agreement"),  pursuant  to which the
Company issued: (a) $20,000,000 aggregate principal amount of its 7.03% Series D
Senior  Notes due  February  15, 2004 (the  "Series D Notes"),  (b)  $75,000,000
aggregate  principal  amount of its 7.28% Series E Senior Notes due February 15,
2009 (the "Series E Notes"),  and (c)  $43,000,000  of its 7.43% Series F Senior
Notes due February 15, 2009 (the "Series F Notes",  and together with the Series
D Notes and the Series E Notes, the "Notes").

     B.  Capitalized  terms  used  herein  shall  have the  respective  meanings
ascribed  thereto in the Existing Note Purchase  Agreement unless herein defined
or the context shall otherwise require.

     C. The Company and the  Noteholders  now desire to amend the Existing  Note
Purchase  Agreement in the respects,  but only in the respects,  hereinafter set
forth.

     D. All requirements of law have been fully complied with and all other acts
and  things  necessary  to make  this  Amendment  a  legal,  valid  and  binding
instrument  according to its terms for the purposes  herein  expressed have been
done or performed.

     NOW,  THEREFORE,  for good  and  valuable  consideration  the  receipt  and
sufficiency of which are hereby acknowledged, the Company and the Noteholders do
hereby agree as follows:

SECTION 1. AMENDMENTS.

<PAGE>

     1.1  Amendment to Section  10.6(b)(i).  Section  10.6(b)(i) of the Existing
Note  Purchase  Agreement  is hereby  amended and  restated  in its  entirety as
follows:

          "(i)   Notwithstanding   the  provisions  of  Section   10.6(a),   the
     determination of whether a Transfer  involves a Substantial  Portion of the
     property  of the Company and the  Restricted  Subsidiaries,  as provided in
     Section 10.6(a)(iii)(A), shall be made without taking into account the same
     proportion of the book value  attributable to the property  subject to such
     Transfer as shall be equal to the proportion of the Net Asset Sale Proceeds
     Amount (the "Designated  Portion") to be applied to either (x) a prepayment
     of the Notes  pursuant to Section 8.2 of this Agreement and a prepayment of
     the Old Notes  pursuant to Section 8.2 of the Old Note Purchase  Agreement,
     pro rata based on the then  outstanding  principal  amount of and  required
     Make-Whole  Amount  (with  respect to the Old Notes,  as defined in the Old
     Note Purchase  Agreement) due with respect to the prepayment of each series
     of the  Notes  and the  Old  Notes  (a  "Prepayment  Transfer")  or (y) the
     acquisition  of assets similar to the assets which were the subject of such
     Transfer (a "Reinvested  Transfer") within one hundred eighty (180) days of
     the consummation of such Transfer, as specified in an Officer's Certificate
     delivered  to  each  holder  prior  to,  or  contemporaneously   with,  the
     consummation of such Transfer."

     1.2  Amendment  to Schedule B.  Schedule B to the  Existing  Note  Purchase
Agreement  is hereby  amended to add,  in the  proper  alphabetical  order,  the
following defined terms:

          "Old  Notes -- means the  Company's  7.17%  Series A Senior  Notes due
     December  30,  2001  in  the  original   aggregate   principal   amount  of
     $25,000,000,  7.17%  Series B Senior  Notes due  December  30,  2002 in the
     original  aggregate  principal  amount of  $27,500,000  and 7.48%  Series C
     Senior  Notes due December  30, 2002 in the  original  aggregate  principal
     amount of $22,500,000 issued pursuant to the Old Note Purchase Agreement."

          "Old  Note  Purchase  Agreement  -- means  each of the  separate  Note
     Purchase  Agreements  between  the Company  and the  purchasers  of the Old
     Notes, dated December 28, 1995, as amended from time to time."

SECTION 2. REPRESENTATIONS AND WARRANTIES OF THE COMPANY.

     To induce the  Noteholders  to execute and deliver  this  Amendment  (which
representations  shall  survive  such  execution  and  delivery),   the  Company
represents and warrants to the Noteholders that:

          (a) the Company is a corporation duly organized,  validly existing and
     in good standing under the laws of the state of Delaware;

          (b) this Amendment has been duly authorized, executed and delivered by
     the  Company  and this  Amendment  constitutes  a legal,  valid and binding
     obligation, contract and agreement of the Company enforceable against it in
     accordance  with  its  terms,  except  as  enforcement  may be  limited  by
     bankruptcy,  insolvency,  reorganization,  moratorium  or  similar  laws or
     equitable principles relating to or limiting creditors' rights generally;

          (c)  the  Existing  Note  Purchase  Agreement,   as  amended  by  this
     Amendment,  constitutes the legal, valid and binding  obligation,  contract
     and agreement of the Company  enforceable against it in accordance with its
     terms,  except as  enforcement  may be limited by  bankruptcy,  insolvency,
     reorganization, moratorium or similar laws or equitable principles relating
     to or limiting creditors' rights generally;

          (d) the  execution,  delivery and  performance  by the Company of this
     Amendment (i) has been duly  authorized by all requisite  corporate  action
     and, if required,  shareholder action, (ii) does not require the consent or
     approval of any  governmental or regulatory body or agency,  and (iii) will
     not (A) violate (1) any  provision of law,  statute,  rule or regulation or
     its certificate of incorporation  or bylaws,  (2) any order of any court or
     any rule,  regulation  or order of any other agency or  government  binding
     upon it, or (3) any provision of any material indenture, agreement or other
     instrument to which it is a party or by which its  properties or assets are
     or may be bound, or (B) result in a breach of or constitute  (alone or with
     due  notice  or lapse  of time or  both) a  default  under  any  indenture,
     agreement or other  instrument  referred to in clause  (iii)(A)(3)  of this
     paragraph (d); and

          (e) as of the date hereof and after giving  effect to this  Amendment,
     no Default or Event of Default has occurred which is continuing.

SECTION 3. MISCELLANEOUS.

     3.1 This Amendment shall be construed in connection with and as part of the
Existing Note Purchase  Agreement,  and except as modified and expressly amended
by this Amendment, all terms, conditions and covenants contained in the Existing
Note  Purchase  Agreement  and the Notes are  hereby  ratified  and shall be and
remain in full force and effect.

     3.2 This  Amendment  constitutes  a contract  between  the  Company and the
Noteholders for the uses and purposes hereinabove set forth, and may be executed
in any  number  of  counterparts,  each  executed  counterpart  constituting  an
original, but all together only one agreement.

     3.3 Whenever any of the parties hereto is referred to, such reference shall
be deemed to include  the  successors  and  assigns of such  party,  and all the
promises  and  agreements  contained  in this  Amendment  by or on behalf of the
Company  and  the  Noteholders  shall  bind  and  inure  to the  benefit  of the
respective successors and assigns of such parties, whether so expressed or not.

     3.4 This Amendment  constitutes the final written  expression of all of the
terms hereof and is a complete and exclusive statement of those terms.

     3.5 This  Amendment  shall be governed by and construed in accordance  with
the internal laws of the State of New York.

     3.6 This  Amendment  shall  become  effective  at such  time as it has been
executed by the Company and the Required Holders.

            [The remainder of this page is intentionally left blank.
                         Next page is signature page.]

<PAGE>

     IN WITNESS  WHEREOF,  the parties  hereto have caused the execution of this
Amendment by duly authorized officers of each as of the date hereof.

                                   SEITEL, INC.

                                   By   /s/ Paul A. Frame
                                        -------------------------------------
                                        Paul A. Frame,
                                        President and Chief Executive Officer

Accepted and Agreed to:

[NOTEHOLDER]

By
  -------------------------------
Name:
Title:

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