Exhibit
      10(x)


    CLASS
      D AMENDMENT


    AMENDMENT
      NO. 1 TO AMENDED
      AND RESTATED OPERATING AGREEMENT OF ATLAS ENERGY RESOURCES, LLC


    THIS
      AMENDMENT NO. 1 TO AMENDED AND
      RESTATED OPERATING AGREEMENT OF ATLAS ENERGY RESOURCES, LLC (this
“Amendment”), dated as of June 29, 2007, is entered into and
      effectuated by the Board of Directors (the “Board”) of Atlas Energy
      Resources, LLC, a Delaware limited liability company (the “Company”),
      pursuant to authority granted to it in Sections 5.5 and 11.1 of the Amended
      and
      Restated Operating Agreement of the Company, dated as of December 18, 2006
      (the “Limited Liability Company Agreement”). Capitalized terms used
      but not defined herein are used as defined in the Limited Liability Company
      Agreement. 

    WHEREAS,
      Section 5.5(a) of the
      Limited Liability Company Agreement provides that the Company may issue
      additional Company Securities for any Company purpose at any time and from
      time
      to time for such consideration and on such terms and conditions as the Board
      shall determine, all without the approval of any Members (subject to the
      provisions of Section 5.6 of the Limited Liability Company Agreement);


    WHEREAS,
      Section 5.5(b) of the
      Limited Liability Company Agreement provides that the Company Securities
      authorized to be issued by the Company pursuant to Section 5.5(a) of the
      Limited Liability Company Agreement may be issued in one or more classes, or
      one
      or more series of any such classes, with such designations, preferences, rights,
      powers and duties (which may be senior to existing classes and series of Company
      Securities) as shall be fixed by the Board; 

    WHEREAS,
      Section 11.1(c)(vii)
      of the Limited Liability Company Agreement provides that the Board, without
      the
      approval of any Member (subject to the provisions of Section 5.6 of the
      Limited Liability Company Agreement), may amend any provision of the Limited
      Liability Company Agreement that the Board determines to be necessary or
      appropriate in connection with the authorization of issuance of any class or
      series of Company Securities pursuant to Section 5.5 of the Limited
      Liability Company Agreement, and the Board has determined that the amendments
      contemplated hereby are necessary or appropriate in connection therewith;


    WHEREAS,
      the Board has determined
      that the issuance of the Class D Units provided for in this Amendment is
      permitted by Section 5.6 of the Limited Liability Company Agreement;


    WHEREAS,
      Section 11.1(c)(iv) of
      the Limited Liability Company Agreement provides that the Board, without the
      approval of any Member, may amend any provision of the Limited Liability Company
      Agreement to reflect a change that the Board determines does not adversely
      affect the Members (including any particular class of Interests as compared
      to
      other classes of Interests) in any material respect, and the Board has
      determined that such amendments contemplated hereby do not adversely affect
      the
      Members in any material respect; and 

    

    
    

    WHEREAS,
      the Board deems it in the
      best interest of the Company to effect this Amendment to provide for
      (i) the issuance of the Class D Units, (ii) the conversion of the
      Class D Units into Common Units in accordance with the terms described herein
      and (iii) such other matters as are provided herein. 

    NOW,
      THEREFORE, it is hereby agreed
      as follows: 

     

    
      	A.	Amendment. The
              Limited Liability Company Agreement is
              hereby amended as follows: 


    

    1.
      Section 1.1 of the Limited
      Liability Company Agreement is hereby amended to add or amend and restate the
      following definitions in the appropriate alphabetical order: 

    “Capital
      Account True-Up
      Election” has the meaning assigned to such term in
      Section 6.1(d)(xii)(C). 

    “Class
      D Distribution Increase
      Date” has the meaning assigned to such term in Section 5.11(h).


    “Class
      D Member Interests”
means the Member Interests represented by the Class D Units. 

    “Class
      D Unit Arrearage”
means, with respect to any Class D Unit, whenever issued, as to any Quarter,
      the
      amount, if any, by which (a) the Initial Quarterly Distribution in respect
      of such Quarter (or, for the period from the Class D Distribution Increase
      Date
      through the Conversion Approval, 115% of the Initial Quarterly Distribution)
      exceeds (b) the sum of all Available Cash distributed with respect to a
      Class D Unit in respect of such Quarter pursuant to Sections 6.4(a)(iii)(x)
      and
      6.4(b)(iii)(x). 

    “Class
      D Unit” means a Unit
      representing a fractional part of the Member Interests of all Members and,
      to
      the extent they are treated as Members hereunder, Assignees, and having the
      rights and obligations specified with respect to Class D Units in this
      Agreement. A “Class D Unit” shall not constitute a Common Unit until such time
      as such Class D Unit is converted into a Common Unit pursuant to the terms
      hereof. 

    “Common
      Unit Arrearage” means, with
      respect to any Common Unit, whenever issued, as to any Quarter during which
      Class D Units are Outstanding, the excess, if any, of (a) the Initial
      Quarterly Distribution with respect to a Common Unit in respect of such Quarter
      over (b) the sum of all Available Cash distributed with respect to a Common
      Unit in respect of such Quarter pursuant to Sections 6.4(a)(i) and 6.4(b)(i).
      

    “Conversion
      Approval” has the
      meaning assigned to such term in Section 5.11(d). 

     

    2


    

    
    

    “Cumulative
      Class D Unit
      Arrearage” means, with respect to any Class D Unit, whenever issued, as of
      the end of any Quarter, the excess, if any, by which (a) the sum resulting
      from adding together the Class D Unit Arrearages for each of the Quarters during
      which any Class D Unit has been Outstanding exceeds (b) the sum of any
      distributions theretofore made to a Class D Unit pursuant to Sections
      6.4(a)(iii)(y), 6.4(b)(iii)(y) and 6.6(d) (including any distributions to be
      made in respect of the last of such Quarters). 

    “Cumulative
      Common Unit
      Arrearage” means, with respect to any Common Unit, whenever issued, and as
      of the end of any Quarter, the excess, if any, of (a) the sum resulting
      from adding together the Common Unit Arrearage as to an Initial Common Unit
      for
      each of the Quarters during which Class D Units are Outstanding ending on or
      before the last day of such Quarter over (b) the sum of any distributions
      theretofore made pursuant to Sections 6.4(a)(ii), 6.4(b)(ii) and 6.6(b).


    “Issue
      Price” means the price
      at which a Unit is purchased from the Company, after taking into account any
      sales commission or underwriting discount charged to the Company and after
      taking into account any other form of discount with respect to the price at
      which a Unit is purchased from the Company. In the case of the Class D Units,
      the Issue Price shall be deemed to be $24.78 per Unit and in the case of the
      Privately Placed Common Units, $25.50 per Unit. 

    “Percentage
      Interest” means,
      as of any date of determination (a) as to any Unitholder holding
      Class A Units, the product obtained by multiplying (i) 2% by
      (ii) the quotient obtained by dividing (A) the number of Class A
      Units held by such Unitholder by (B) the total number of Outstanding
      Class A Units; (b) as to any Unitholder holding Common Units or Class
      D Units, the product obtained by multiplying (i) 98% by (ii) the
      quotient obtained by dividing (A) the number of Common Units and/or Class D
      Units held by such Unitholder by (B) the total number of all Outstanding
      Common Units and Class D Units, and (c) as to the holders of other Company
      Securities issued by the Company in accordance with Section 5.5, the
      percentage established as a part of such issuance. 

    “Per
      Unit Capital Amount”
means, as of any date of determination, the Capital Account, stated on
      a per
      Unit basis, as the case may be, underlying any Common Unit (other than a
      Privately Placed Common Unit), Class A Unit, Class D Unit or Privately
      Placed Common Unit, as the case may be, held by a Person. 

    “Private
      Placement Value”
means with respect to the Class D Units and the Privately Placed Common
      Units,
      $34.19 per Unit. 

     

    3


    

    
    

    “Privately
      Placed Common
      Units” means the Common Units issued pursuant to the Unit Purchase
      Agreement. 

    “Unit”
means
      a Company
      Security that is designated as a “Unit” and shall include Class A Units,
      Class D Units and Common Units, but shall not include the Management Incentive
      Interests. 

    “Unit
      Purchase Agreement”
means the Class D Unit and Common Unit Purchase Agreement dated as of
      May 18, 2007 between the Company and the purchasers named therein.


    2.
      Section 1.1 of the Limited
      Liability Company Agreement is hereby further amended to add a new sentence
      at
      the end of the definition of “Common Unit” as follows: 

    The
      term “Common Unit” does not
      include a Class D Unit prior to its conversion into a Common Unit pursuant
      to
      this Agreement. 

    3.
      Article IV of the Limited
      Liability Company Agreement is hereby amended to add a new Section 4.6(e)
      as follows: 

    (e)
      The transfer of (1) a Class
      D Unit that has been converted into a Common Unit pursuant to Section 5.11
      or (2) a Privately Placed Common Unit shall be subject to the restrictions
      imposed by Section 6.9. 

    4.
      Section 5.4(a) of the
      Limited Liability Company Agreement is hereby amended to add the following
      at
      the end of such section: 

    The
      initial Capital Account balance
      in respect of each Class D Unit shall be the Private Placement Value for such
      Class D Unit, and the initial Capital Account balance of each holder of Class
      D
      Units in respect of all Class D Units held shall be the product of such initial
      balance for a Class D Unit multiplied by the number of Class D Units held by
      such holder. The initial Capital Account balance in respect of each
      Privately Placed Common Unit shall be the Private Placement Value for such
      Privately Placed Common Unit, and the initial Capital Account balance of each
      holder of Privately Placed Common Units in respect of all Privately Placed
      Common Units held shall be the product of such initial balance for a Privately
      Placed Common Unit multiplied by the number of Privately Placed Common Units
      held by such holder. Immediately following the creation of a Capital
      Account balance in respect of each Class D Unit, each holder acquiring a Class
      D
      Unit at original issuance shall be deemed to have received a cash distribution
      in respect of such Class D Units in an amount equal to the product of
      (x) the total number of Class D Units so acquired by such holder multiplied
      by (y) the difference between the Private Placement Value and the Issue
      Price of a Class D Unit. Immediately following the creation of a Capital
      Account balance in respect of each Privately Placed Common Unit, each Unitholder
      acquiring a Privately Placed Common Unit at original issuance shall be deemed
      to
      have received a cash distribution in respect of such Privately Placed Common
      Units in an amount equal to the product of (x) the total number of


     

    4


    

    
    

    Privately
      Placed Common Units so
      acquired by such Unitholder multiplied by (y) the difference between the
      Private Placement Value and the Issue Price of a Privately Placed Common
      Unit. The purpose of the four preceding sentences is to provide the initial
      purchasers of Class D Units and Privately Placed Common Units with a net Capital
      Account in the Class D Units and Privately Placed Common Units on the date
      of
      purchase equal to the Issue Price paid by those purchasers for the Class D
      Units
      and Privately Placed Common Units. 

    5.
      Section 5.4(c)(i) of the
      Limited Liability Company Agreement is hereby amended to add the following
      at
      the end of such section: 

    Any
      adjustments that are made under
      this paragraph in connection with the issuance of the Class D Units or the
      Privately Placed Common Units shall be based on the Private Placement Value
      of
      the Class D Units and the Privately Placed Common Units. 

    6.
      Article V of the Limited
      Liability Company Agreement is hereby amended to add a new Section 5.11
      creating a new series of Company Securities as follows: 

    Section 5.11
Establishment
      of Class D Units. 

    (a)
General. The
      Board
      hereby designates and creates a series of Company Securities to be designated
      as
“Class D Units” and consisting of a total of 16,702,828 Class D Units, and fixes
      the designations, preferences and relative, participating, optional or other
      special rights, powers and duties of holders of the Class D Units as set forth
      in this Section 5.11. A form of Certificate Evidencing Class D Units is
      attached as Exhibit 4.2. 

    (b)
Rights
      of Class D Units.
During the period commencing upon issuance of the Class D Units and ending
      on the upon Conversion Approval (or that later time specified in this
      Section 5.11(b)), unless amended pursuant to Section 5.11(h) hereof:


    (i)
Allocations.
Except
      as
      otherwise provided in this Agreement, all items of Company income, gain, loss,
      deduction and credit shall be allocated to the Class D Units to the same extent
      as such items would be so allocated if such Class D Units were Common Units
      (other than Privately Placed Common Units) that were then Outstanding.


    (ii)
Distributions.
Except
      as
      otherwise specified in this Agreement, Class D Units shall have the right to
      the
      distributions specified in Article VI of this Agreement. 

    (iii)
Elimination
      of Cumulative
      Class D Unit Arrearages Upon Conversion. If a Cumulative Class D Unit
      Arrearage

     

    5


    

    
    

    exists
      at the time of Conversion
      Approval, Available Cash shall be distributed 98% to the Unitholders holding
      Class D Units, Pro Rata, and 2% to the holders of Class A Units, Pro Rata,
      until there has been distributed in respect of each Class D Unit then
      Outstanding an amount equal to the Cumulative Class D Unit Arrearage as of
      such
      date. This distribution shall not be deemed a distribution on a Common Unit,
      but
      the satisfaction of prior entitlements of the holders of Class D Units as of
      Conversion Approval. For the taxable year in which the distribution is made,
      if
      not previously allocated, each Person receiving such distribution shall be
      allocated items of gross income in an amount equal to such distribution as
      provided in Section 6.1(d)(iii)(C). 

    (c)
      [Reserved] 

    (d)
Vote
      of
      Unitholders. Except as provided in this Section 5.11, the Class D
      Units are not convertible into Common Units. The Board shall, as promptly
      as practicable following the issuance of the Class D Units, but in any event
      not
      later than 135 days after the date hereof, take such actions as
      may be necessary or appropriate to submit to a vote or consent of the holders
      of
      the Units the approval of a change in the terms of the Class D Units to provide
      that each Class D Unit will automatically convert into one Common Unit (subject
      to appropriate adjustment in the event of any split-up, combination or similar
      event affecting the Common Units that occurs prior to the conversion of the
      Class D Units), except that for purposes of this Section 5.11(d) the term
“Unitholders” shall not include the holders of Class D Units (the “Conversion
      Approval”). Effective immediately upon the Conversion Approval by the
      Unitholders, the issuance of additional Common Units to be issued upon such
      automatic conversion shall be approved without any further action by the holders
      thereof. The vote or consent required for such approval will be the
      requisite vote required under this Agreement and under the rules or staff
      interpretations of the National Securities Exchange on which the Common Units
      are listed or admitted to trading for the listing or admission to trading of
      the
      Common Units that would be issued upon any such conversion. Upon receipt of
      such approval and compliance with Section 5.11(f), the terms of the Class D
      Units will be changed, automatically and without further action, so that each
      Class D Unit is converted into one Common Unit and, immediately thereafter,
      none
      of the Class D Units shall be Outstanding. 

    (e)
Change
      in Rules of National
      Securities Exchange. If at any time (i) the rules of the National
      Securities Exchange on which the Common Units are listed or admitted to trading
      or the staff interpretations of such rules are changed or (ii) facts or
      circumstances arise so that no vote or consent of Unitholders (except that
      for
      purposes of this Section 5.11(e) the term “Unitholders” shall not include
      the holders of the Class D Units) is required as a condition to the listing
      or
      admission to trading of the Common Units that would be issued upon any
      conversion of any Class D Units into Common Units as provided in
      Section 5.11(d), the terms of such Class D Units will be changed so that
      each Class D Unit is converted (without further action or any vote of any
      Unitholders other than 

     

    6


    

    
    

    compliance
      with
      Section 5.11(f)) into one Common Unit (subject to appropriate adjustment in
      the event of any split-up, combination or similar event affecting the Common
      Units that occurs prior to the conversion of the Class D Units) and, immediately
      thereafter, none of the Class D Units shall be Outstanding. 

    (f)
Surrender
      of
      Certificates. Upon receipt of the approval of the holders of the Units
      (other than holders of the Class D Units, who do not vote as part of the
      Conversion Approval) to convert the Class D Units into Common Units in
      accordance with Section 5.11(d) or a change in rules of the National
      Securities Exchange or a change in facts and circumstances as described in
      Section 5.11(e), the Board shall give the holders of the Class D Units
      prompt notice of such approval or change and, subject to Section 6.9, each
      holder of Class D Units shall promptly surrender the Class D Unit Certificates
      therefor, duly endorsed, at the office of the Company or of any transfer agent
      for the Class D Units. In the case of any such conversion, the Company
      shall, as soon as practicable thereafter, issue and deliver at such office
      to
      such holder of Class D Units one or more Unit Certificates, registered in the
      name of such holder, for the number of Common Units to which such holder shall
      be entitled as aforesaid. Such conversion shall be deemed to have been made
      as of the date of the event specified in Section 5.11(d) or
      Section 5.11(e), as the case may be, and the Person entitled to receive the
      Common Units issuable upon such conversion shall be treated for all purposes
      as
      the record holder of such Units on said date. 

    (g)
Voting
      Rights. The
      Class D Units are non-voting, except that the Class D Units shall be entitled
      to
      vote as a separate class on any matter that adversely affects the rights or
      preferences of the Class D Units in relation to other classes of Interests
      (including as a result of a merger or consolidation) or as required by
      law. The approval of a majority of the Class D Units shall be required to
      approve any matter for which the holders of the Class D Units are entitled
      to
      vote. 

    (h)
Automatic
      Provisions. If
      the Conversion Approval has not occurred within 135 days after the date hereof,
      then, effective as of the next succeeding day (the “Class D Distribution
      Increase Date”) until the Conversion Approval is obtained, Section 5.11(b)
      will be deemed to be amended in its entirety, automatically and without further
      action, as follows: 

    (b)
Rights
      of Class D Units.
Prior to the Conversion Approval (or the later date specified in this
      Section 5.11(b)): 

    (i)
Allocations.
Except
      as
      otherwise provided in this Agreement, all items of Company income, gain, loss,
      deduction and credit shall be allocated to the Class D Units to the same extent
      as such items would be so allocated if such Class D Units were Common Units
      (other than Privately Placed Common Units) that were then Outstanding.


    (ii)
Distributions.
Except
      as
      otherwise specified in this Agreement, Class D Units shall have the right to
      the
      distributions specified in Article VI of this Agreement. Notwithstanding the
      provisions of Article VI: 

     

    7


    

    
    

    (A)
      Sections 6.4(a)(iii) and
      6.4(b)(iii) shall be applied by substituting “115%” for “100%”. 

    (B)
      Each Class D Unit shall be
      entitled to 115% of the amount distributed per Common Unit pursuant to Sections
      6.4(a)(iv), 6.4(b)(iv), 6.4(b)(v) and 6.4(b)(vi). 

    (iii)
Elimination
      of Cumulative
      Class D Unit Arrearages Upon Conversion. If a Cumulative Class D Unit
      Arrearage exists at the time of Conversion Approval, Available Cash shall be
      distributed 98% to the Unitholders holding Class D Units, Pro Rata, and 2%
      to
      the holders of Class A Units, Pro Rata, until there has been distributed in
      respect of each Class D Unit then Outstanding an amount equal to the Cumulative
      Class D Unit Arrearage as of such date. This distribution shall not be deemed
      a
      distribution on a Common Unit, but the satisfaction of prior entitlements of
      the
      holders of Class D Units as of Conversion Approval. For the taxable year in
      which the distribution is made, if not previously allocated, each Person
      receiving such distribution shall be allocated items of gross income in an
      amount equal to such distribution as provided in Section 6.1(d)(iii)(C).


    7.
      Section 6.1(c)(ii) of the
      Limited Liability Company Agreement is hereby amended and restated as follows:
      

    (ii)
      If a Net Termination Loss is
      recognized (or deemed recognized pursuant to Section 5.4(c)), such Net
      Termination Loss shall be allocated among the Members in the following manner:
      

    (A)
      First, 2% to the holders of
      Class A Units, Pro Rata, and 98% to the holders of Class D Units, Pro Rata,
      until the Capital Account in respect to each Class D Unit then Outstanding
      has
      been reduced to zero; 

    (B)
      Second, 2% to the holders of
      Class A Units, Pro Rata, and 98% to the holders of Common Units, Pro Rata,
      until the Capital Account in respect to each Common Unit then Outstanding has
      been reduced to zero; and 

    (C)
      Third, the balance, if any, to
      all Unitholders in accordance with their respective Percentage Interests.


     

    8


    

    
    

    8.
      Article VI of the Limited
      Liability Company Agreement is hereby amended to add a new
      Section 6.1(d)(iii)(C) as follows: 

    (C)
      After the application of
      Sections 6.1(d)(iii)(A) and (B), if the amount of cash or the Net Agreed Value
      of any property distributed (except cash or property distributed or deemed
      distributed pursuant to Section 5.4(a) of this Agreement with respect to
      Class D Units or Privately Placed Common Units, or Section 10.3 of this
      Agreement) to any Unitholder with respect to its Units for a taxable year is
      greater (on a per Unit basis) than the amount of cash or the Net Agreed Value
      of
      property distributed to the other Unitholders with respect to their Units (on
      a
      per Unit basis), then each Unitholder receiving such greater cash or property
      distribution shall be allocated gross income in an amount equal to the product
      of (a) the amount by which the distribution (on a per Unit basis) to such
      Unitholder exceeds the distribution (on a per Unit basis) to the Unitholders
      receiving the smallest distribution and (b) the number of Units owned by
      the Unitholder receiving the greater distribution. 

    9.
      Article VI of the Limited
      Liability Company Agreement is hereby amended to add a new
      Section 6.1(d)(xii) as follows: 

    (xii)
Allocations
      for Class D
      Units and Privately Placed Common Units. 

    (A)
      With respect to any taxable
      period of the Company ending upon, or after, a Book-Up Event, a Book-Down Event
      or a sale of all or substantially all of the assets of the Company occurring
      after the date of issuance of the Class D Units and the Privately Placed Common
      Units, Company items of income or gain for such taxable period shall be
      allocated 100% (1) to the Members holding Class D Units or converted Class
      D Units that are Outstanding as of the time of such event in proportion to
      the
      number of Class D Units or converted Class D Units held by such Members, until
      each such Member has been allocated the amount that increases the Capital
      Account of such Class D Unit or converted Class D Unit to the Per Unit Capital
      Amount for a then outstanding Common Unit (other than a converted Class D Unit
      or a Privately Placed Common Unit) and (2) to the Members holding Privately
      Placed Common Units that are Outstanding as of the time of such event in
      proportion to the number of Privately Placed Common Units held by such Members,
      until each such Member has been allocated the amount that increases the Capital
      Account of such Privately Placed Common Unit to the Per Unit Capital Amount
      for
      a then outstanding Common Unit (other than a Privately Placed Common Unit or
      a
      Class D Unit). 

    (B)
      With respect to any taxable
      period of the Company ending upon, or after, the transfer of converted Class
      D
      Units or Privately Placed Common Units to a Person that is not an Affiliate
      of
      the holder, Company items of income or gain for such taxable period shall be
      allocated 100% (1) to the Members transferring such converted Class D Units
      in proportion to 

     

    9


    

    
    

    the
      number of converted Class D
      Units transferred by such Members, until each such Member has been allocated
      the
      amount that increases the Capital Account of such converted Class D Unit to
      the
      Per Unit Capital Amount for a then outstanding Common Unit (other than a
      converted Class D Unit or a Privately Placed Common Unit) and (2) to the
      Members transferring such Privately Placed Common Units in proportion to the
      number of Privately Placed Common Units transferred by such Members, until
      each
      such Member has been allocated the amount that increases the Capital Account
      of
      such Privately Placed Common Unit to the Per Unit Capital Amount for a then
      outstanding Common Unit (other than a Privately Placed Common Unit or a
      converted Class D Unit). 

    (C)
      With respect to the first
      taxable period of the Company ending upon, or after, the date of issuance of
      the
      Class D Units or the Privately Placed Common Units, at the election of a Member
      holding Class D Units or Privately Placed Common Units (the “Capital Account
      True-Up Election”), items of income or gain for such taxable period shall be
      allocated 100% to the Members making such Capital Account True-Up Election
      with
      respect to Class D Units or Privately Placed Common Units held by such Members,
      until each such Member has been allocated the amount that increases the Capital
      Account of such Class D Unit or Privately Placed Common Unit to the Per Unit
      Capital Amount for a then outstanding Common Unit (other than a Class D Unit
      or
      a Privately Placed Common Unit). 

    10.
      Section 6.4 of the Limited
      Liability Company Agreement is amended to read as follows: 

    Section 6.4
      Distributions of
      Available Cash from Operating Surplus. 

    (a)
During
      the MII Vesting
      Period. Available Cash with respect to any Quarter ending prior to or on the
      date of the end of the MII Vesting Period that is deemed to be Operating Surplus
      pursuant to the provisions of Section 6.3 or Section 6.6 shall,
      subject to Section 8-607 of the Delaware Act, be distributed, except as
      otherwise required by Section 5.5(b) in respect of other Company Securities
      issued pursuant thereto, as follows: 

    (i)
      First, (A) 2% to the
      holder(s) of the Class A Units, Pro Rata and (B) 98% to the holders of
      the Common Units, Pro Rata until there has been distributed in respect of each
      Common Unit then Outstanding an amount equal to the Initial Quarterly
      Distribution for such Quarter; 

    (ii)
      Second, (A) 2% to the
      holder(s) of the Class A Units, Pro Rata and (B) 98% to the holders of
      the Common Units, Pro Rata until there has been distributed in respect of each
      Common Unit then Outstanding an amount equal to the Cumulative Common Unit
      Arrearage existing with respect to such Quarter; 

     

    10


    

    
    

    (iii)
      Third, (x) (A) 2% to
      the holder(s) of the Class A Units, Pro Rata and (B) 98% to the
      holders of the Class D Units, Pro Rata, until there has been distributed in
      respect of each Class D Unit then Outstanding an amount equal to 100% of the
      Initial Quarterly Distribution for such Quarter; and (y) (A) 2% to the
      holder(s) of the Class A Units, Pro Rata and (B) 98% to the holders of
      the Class D Units, Pro Rata, until there has been distributed in respect of
      each
      Class D Unit then Outstanding an amount equal to the Cumulative Class D Unit
      Arrearage, if any, existing with respect to such Quarter; 

    (iv)
      Fourth, (A) 2% to the
      holder(s) of the Class A Units, Pro Rata and (B) 98% to the holders of
      the Common Units and Class D Units, Pro Rata. 

    (b)
After
      the MII Vesting
      Period. Available Cash with respect to each Quarter after the MII Vesting
      Period that is deemed to be Operating Surplus pursuant to the provisions of
      Section 6.3 or Section 6.6 shall, subject to
      Section 18-607 of the Delaware Act, be distributed, except as otherwise
      required by Section 5.5(b) in respect of additional Company
      Securities issued pursuant thereto, as follows: 

    (i)
      First, (A) 2% to the
      holder(s) of the Class A Units, Pro Rata and (B) 98% to the holders of
      the Common Units, Pro Rata until there has been distributed in respect of each
      Common Unit then Outstanding an amount equal to the Initial Quarterly
      Distribution for such Quarter; 

    (ii)
      Second, (A) 2% to the
      holder(s) of the Class A Units, Pro Rata and (B) 98% to the holders of
      the Common Units, Pro Rata until there has been distributed in respect of each
      Common Unit then Outstanding an amount equal to the Cumulative Common Unit
      Arrearage existing with respect to such Quarter; 

    (iii)
      Third, (x) (A) 2% to
      the holder(s) of the Class A Units, Pro Rata and (B) 98% to the
      holders of the Class D Units, Pro Rata, until there has been distributed in
      respect of each Class D Unit then Outstanding an amount equal to 100% of the
      Initial Quarterly Distribution for such Quarter; and (y) (A) 2% to the
      holder(s) of the Class A Units, Pro Rata and (B) 98% to the holders of
      the Class D Units, Pro Rata, until there has been distributed in respect of
      each
      Class D Unit then Outstanding an amount equal to the Cumulative Class D Unit
      Arrearage, if any, existing with respect to such Quarter; 

     

    11


    

    
    

    (iv)
      Fourth, (A) 2% to the
      holders of Class A Units, Pro Rata, and (B) 98% to the holders of
      Common Units and Class D Units, Pro Rata, until there has been distributed
      in
      respect of each Class A Unit, each Class D Unit and each Common Unit then
      Outstanding an amount equal to the Initial Quarterly Distribution for such
      Quarter plus $0.06 (the “First Target Distribution”); 

    (v)
      Fifth, (A) 2% to the
      holders of the Class A Units, Pro Rata, (B) 83% to the holders of the
      Common Units and Class D Units, Pro Rata, and (C) 15% to the holders of the
      Management Incentive Interests, Pro Rata, until there has been distributed
      in
      respect of each Class A Unit, each Class D Unit and each Common Unit then
      Outstanding an amount equal to the Initial Quarterly Distribution for such
      Quarter plus $0.17 (the “Second Target Distribution); and 

    (vi)
      Thereafter, (A) 2% to the
      holders of the Class A Units, Pro Rata, (B) 73% to the holders of the
      Common Units and Class D Units, Pro Rata, and (C) 25% to the holders of the
      Management Incentive Interests, Pro Rata. 

    11.
      Section 6.6 of the Limited
      Liability Company Agreement is amended to read as follows: 

    Section 6.6
Distributions
      of
      Available Cash from Capital Surplus

    Available
      Cash that is deemed to be
      Capital Surplus pursuant to the provisions of Section 6.3(a) shall,
      subject to Section 18-607 of the Delaware Act, be distributed, unless the
      provisions of Section 6.3 require otherwise, be distributed as
      follows: 

    (a)
      100% to the holders of Common
      Units, Pro Rata, until a hypothetical holder of a Common Unit acquired on the
      Closing Date has received with respect to such Common Unit, during the period
      since the Closing Date through such date, distributions of Available Cash that
      are deemed to be Capital Surplus in an aggregate amount equal to the Initial
      Unit Price; 

    (b)
      100% to the holders of Common
      Units, Pro Rata, until there has been distributed in respect of each Common
      Unit
      then Outstanding an amount equal to the Cumulative Common Unit Arrearage.
      Thereafter, all Available Cash shall be distributed as if it were Operating
      Surplus and shall be distributed in accordance with Section 6.4.


     

    12


    

    
    

    (c)
      100% to the holders of Class D
      Units, Pro Rata, until a hypothetical holder of a Class D Unit acquired on
      the
      Closing Date has received with respect to such Class D Unit, during the period
      since the date Class D Units were originally issued through such date,
      distributions of Available Cash that are deemed to be Capital Surplus in an
      aggregate amount equal to the Initial Unit Price; 

    (d)
      100% to the holders of Class D
      Units, Pro Rata, until there has been distributed in respect of each Class
      D
      Unit then Outstanding an amount equal to the Cumulative Class D Unit Arrearage;
      and 

    (e)
      Thereafter, all Available Cash
      shall be distributed as if it were Operating Surplus and shall be distributed
      in
      accordance with Section 6.4. 

    12.
      Article VI is hereby amended to
      add a new Section 6.9 as follows: 

    Section 6.9
Special
      Provisions Relating to Holders of Converted Class D Units and Privately Placed
      Common Units. A holder of (1) a Privately Placed Common Unit or
      (2) a Class D Unit that has converted into a Common Unit pursuant to
      Section 5.11 shall be required to provide notice to the Board of the number
      of Privately Placed Common Units or converted Class D Units transferred by
      such
      holder no later than the last Business Day of the calendar year during which
      such transfer occurred, unless (x) the transfer is to an Affiliate of the
      holder or (y) by virtue of the application of Section 6.1(d)(xii)(B)
      to a prior transfer of the Common Unit or the application of
      Section 6.1(d)(xii)(A) or Section 6.1(d)(xii)(C), the Board has
      previously determined, based on advice of counsel, that the Privately Placed
      Common Unit or converted Class D Unit should have, as a substantive matter,
      like
      intrinsic economic and federal income tax characteristics of an Initial Common
      Unit; provided, that such holder may cure any failure to provide such notice
      by
      providing such notice within 20 days of the last Business Day of such calendar
      year. The sole and exclusive remedy for any holder’s failure to provide any
      such notice shall be the enforcement of the remedy of specific performance
      against such holder and there will be no monetary damages. In connection
      with the condition imposed by this Section 6.9, the Board shall take
      whatever steps are required to provide economic uniformity to the Privately
      Placed Common Units and converted Class D Units in preparation for a transfer
      thereof, including the application of Section 6.1(d)(xii)(B); provided,
      however, that no such steps 

     

    13


    

    
    

    may
      be taken that would have a
      material adverse effect on the Unitholders holding Common Units represented
      by
      Certificates. 

    B.
Agreement
      in
      Effect. Except as hereby amended, the Limited Liability Company
      Agreement shall remain in full force and effect. 

    C.
Applicable
      Law. This
      Amendment shall be construed in accordance with and governed by the laws of
      the
      State of Delaware, without regard to principles of conflicts of laws.


    D.
Invalidity
      of
      Provisions. If any provision of this Amendment is or becomes invalid,
      illegal or unenforceable in any respect, the validity, legality and
      enforceability of the remaining provisions contained herein shall not be
      affected thereby. 

     

    14


    

    
    

    IN
      WITNESS WHEREOF, this Amendment
      has been executed as of the date first written above. 

     

    
      	
            	
            	
            
	ATLAS
              ENERGY RESOURCES, LLC
	
            	
            
	
              By:

            	 	
              /s/
                Matthew A.
                Jones

            
	Name:	 	Matthew
              A. Jones
	Title:	 	CFO


    

    [Signature
      Page to Form of Class D
      Amendment] 

     

    15


    

    
    

    Exhibit
      4.2


     

    
      	
            	
            	
            	
            	
            
	
            	  	Certificate
              Evidencing Class D Units	  	
            
	Certificate No.         	  	Representing
              Limited Liability Company Interests
              in	  	Class D Units
	
            	  	Atlas
              Energy Resources, LLC	  	
            


    

    In
      accordance with
      Section 4.1 of the Amended and Restated Operating Agreement of Atlas Energy
      Resources, LLC, as amended, supplemented or restated from time to time (the
      “Company Agreement”), Atlas Energy Resources, LLC, a Delaware limited liability
      company (the “Company”), hereby certifies that
                                        
         (the “Holder”) is the
      registered owner of
            
      CLASS D UNITS representing limited liability company interests in the
      Company (the “Class D Units”) transferable on the books of the Company,
      in person or by duly authorized attorney, upon surrender of this Certificate
      properly endorsed. The rights, preferences and limitations of the Class D
      Units are set forth in, and this Certificate and the Class D Units represented
      hereby are issued and shall in all respects be subject to the terms and
      provisions of, the Company Agreement. Copies of the Company Agreement are
      on file at, and will be furnished without charge on delivery of written request
      to the Company at, the principal office of the Company located at 311 Rouser
      Road, Moon Township, PA 15108. Capitalized terms used herein but not
      defined shall have the meanings given them in the Company Agreement.


    The
      Holder, by accepting this
      Certificate, is deemed to have (i) requested admission as, and agreed to
      become, a Member and to have agreed to comply with and be bound by and to have
      executed the Company Agreement, (ii) represented and warranted that the
      Holder has all right, power and authority and, if an individual, the capacity
      necessary to enter into the Company Agreement, (iii) granted the powers of
      attorney provided for in the Company Agreement and (iv) made the waivers
      and given the consents and approvals contained in the Company Agreement.


    This
      Certificate shall not be valid
      for any purpose unless it has been signed by duly authorized officers of the
      Company. 

     

    
      	
            	
            	
            	
            	
            
	
              Dated: _____________,
                2007

            	 	ATLAS
              ENERGY RESOURCES, LLC
	
            	
            	
            
	
            	 	By:	 	
               

            
	
            	 	
            	 	
              Chairman,
                President and
                Chief

              Executive
                Officer

            
	
            	
            	
            
	
            	 	By:	 	
               

            
	
            	 	
            	 	Secretary


    

    “THESE
      SECURITIES HAVE NOT BEEN
      REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED. THESE SECURITIES MAY
      NOT BE SOLD, OFFERED FOR SALE, PLEDGED (EXCEPT IN CONNECTION WITH A BONA FIDE
      MARGIN ACCOUNT OR OTHER LOAN OR FINANCING ARRANGEMENT SECURED BY THESE
      SECURITIES) OR HYPOTHECATED IN THE ABSENCE OF A REGISTRATION STATEMENT IN EFFECT
      WITH RESPECT TO THE SECURITIES UNDER SUCH ACT OR PURSUANT TO AN EXEMPTION FROM
      REGISTRATION THEREUNDER AND, IN THE CASE OF A TRANSACTION EXEMPT FROM
      REGISTRATION, UNLESS SOLD PURSUANT TO RULE 144 UNDER SUCH ACT OR THE ISSUER
      HAS
      RECEIVED DOCUMENTATION REASONABLY SATISFACTORY TO IT THAT SUCH TRANSACTION
      DOES
      NOT REQUIRE REGISTRATION UNDER SUCH ACT.” FOR THE AVOIDANCE OF DOUBT, THE
      PURCHASED UNITS AND THE PURCHASED CLASS D UNITS MAY BE PLEDGED IN CONNECTION
      WITH A BONA FIDE MARGIN ACCOUNT OR OTHER LOAN OR FINANCING ARRANGEMENT SECURED
      BY SUCH PURCHASED UNITS OR PURCHASED CLASS D UNITS AND SUCH PLEDGE SHALL NOT
      BE
      DEEMED TO BE A TRANSFER, SALE OR ASSIGNMENT OF SUCH PURCHASED UNITS OR PURCHASED
      CLASS D UNITS, AND NO BUYER EFFECTING SUCH A PLEDGE SHALL BE REQUIRED TO PROVIDE
      ATLAS ENERGY WITH ANY NOTICE THEREOF OR OTHERWISE MAKE ANY DELIVERY TO ATLAS
      ENERGY PURSUANT TO THIS AGREEMENT OR ANY OTHER BASIC
      DOCUMENT. 

     

    16


    

    
    

    Atlas
      Energy Resources, LLC


    [Reverse
      of Certificate]


    ABBREVIATIONS
      

    The
      following abbreviations, when
      used in the inscription on the face of this Certificate, shall be construed
      as
      follows according to applicable laws or regulations: 

     

    
      	
            	
            	
            	
            	
            	
            	
            	
            	
            	
            	
            	
            	
            
	TEN COM	 	–	 	as tenants in common	  	UNIF GIFT MIN ACT–	  	
               

            	  	Custodian	  	
               

            
	TEN
              ENT	 	–	 	as
              tenants by the entireties	  	
            	  	(Cust)	  	
            	  	(Minor)
	JT
              TEN	 	–	 	as joint tenants with right of
              survivorship and not as tenants in common	  	
              under Uniform Gifts to Minors

              Act

            	  	
               

            	  	
            	  	
            
	
            	 	
            	 	
            	  	
            	  	(State)	  	
            	  	
            
	
            	 	
            	 	
            	  	
            	  	
            	  	
            	  	
            
	Additional
              abbreviations, though not in the above list, may also be
              used.	  	
            	  	
            


    

    ASSIGNMENT
      OF CLASS D UNITS


    In


    Atlas
      Energy Resources, LLC


     

    
      	
            	
            	
            	
            	
            
	FOR
              VALUE
              RECEIVED,	 	
               

            	 	hereby
              assigns, conveys, sells and transfers unto
	
               

               

            
	(Please
              print or typewrite name and address of Assignee)	 	
            


    

     

    
      	
            	
            	
            
	
               

            	 	
               

            
	
            	
            
	
            	 	(Please
              insert Social Security or other identifying number of
              Assignee)


    

     

    
      	
            	
            	
            	
            	
            
	
            
	                                
              Class D Units representing limited liability company interests evidenced
              by this Certificate, subject to the Company Agreement, and does hereby
              irrevocably constitute and appoint
                                                      
                   as its attorney-in-fact with full power of
              substitution to transfer the same on the books of Atlas Energy Resources,
              LLC.
	
            	
            
	Date:                                     
                                                 	 	NOTE:
              The signature to any endorsement hereon must correspond with
              the name as written upon the face of this Certificate in every particular,
              without alteration, enlargement or change.
	
            	
            	
            
	
            	 	
            	 	
               

            
	The
              signature(s) should be guaranteed by an “eligible guarantor
              institution” as defined in Rule 17Ad-15 under the Securities and Exchange
              Act of 1934, as amended	 	(Signature)
	
            	
            
	
            	 	
               

            
	
            	 	
            	 	(Signature)


    

    SIGNATURE(S)
      GUARANTEED:


    No
      assignment or transfer of the
      Class D Units evidenced hereby will be registered on the books of the Company
      unless the Certificate evidencing the Class D Units to be transferred is
      surrendered for registration or transfer. 

     

    17