FORM OF 6.150% DEBENTURE DUE 2037

Exhibit 4.2

FORM OF 6.150% DEBENTURE DUE 2037

Unless this certificate is presented by an authorized representative of The Depository Trust Company, a New York corporation (“DTC”), to the issuer or its agent for registration of transfer, exchange or payment, and any certificate issued is registered in the name of Cede & Co. or such other name as is requested by an authorized representative of DTC (and any payment is made to Cede & Co. or to such other entity as is requested by an authorized representative of DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL since the registered owner hereof, Cede & Co., has an interest herein.

THIS SECURITY IS A GLOBAL SECURITY AS REFERRED TO IN THE INDENTURE HEREINAFTER REFERENCED. UNLESS AND UNTIL IT IS EXCHANGED IN WHOLE OR IN PART FOR THE INDIVIDUAL SECURITIES REPRESENTED HEREBY, THIS GLOBAL SECURITY MAY NOT BE TRANSFERRED EXCEPT AS A WHOLE BY THE DEPOSITARY TO A NOMINEE OF THE DEPOSITARY OR BY A NOMINEE OF THE DEPOSITARY TO THE DEPOSITARY OR ANOTHER NOMINEE OF THE DEPOSITARY OR BY THE DEPOSITARY OR ANY SUCH NOMINEE TO A SUCCESSOR DEPOSITARY OR A NOMINEE OF SUCH SUCCESSOR DEPOSITARY.

UNION PACIFIC CORPORATION

6.150% Debenture due 2037

UNION PACIFIC CORPORATION, a corporation duly organized and existing under the laws of the State of Utah (herein called the “Company”, which term includes any successor under the Indenture hereinafter referred to), for value received, hereby promises to pay to

Cede & Co.

or registered assigns, the principal sum of $250,000,000 at the office or agency of the Company in the Borough of Manhattan, The City of New York, on May 1, 2037 in such coin or currency of the United States of America as at the time of payment shall be legal tender for the payment of public and private debts, and to pay interest on said principal sum at the rate per annum specified above semiannually on May 1 and November 1 of each year (each, an “Interest Payment Date”), commencing November 1, 2007. Interest shall be paid from the Interest Payment Date, as the case may be, next preceding the date of this Denbenture to which interest on the Debentures has been paid or duly provided for (unless the date hereof is the date to which interest on the Debentures has been paid or duly provided for, in which case from the date of this Debenture), or, if no interest has been paid on the Debentures or duly provided for, from April 18, 2007 until payment of said principal sum has been made or duly provided for. Notwithstanding the foregoing, if the date hereof is after April 15 or October 15 (each, a “Regular Record Date”) and before the next succeeding Interest Payment Date, this Debenture shall bear interest from such Interest Payment Date, as the case may be; provided, however, that if the Company shall default

in the payment of interest due on such Interest Payment Date, then this Debenture shall bear interest from the next preceding Interest Payment Date to which interest on the Debentures has been paid or duly provided for, or if no interest has been paid on the Debentures or duly provided for, from April 18, 2007. The interest so payable, and punctually paid or duly provided for, on any Interest Payment Date will, except as provided in the Indenture dated as of April 1, 1999 (herein called the “Indenture”), between the Company and The Bank of New York, as successor to JPMorgan Chase Bank N.A. (formerly The Chase Manhattan Bank), as Trustee (herein called the “Trustee”), be paid to the Person in whose name this Debenture (or one or more Predecessor Securities) is registered at the close of business on the next preceding Regular Record Date, whether or not a Business Day, and may, at the option of the Company, be paid by check mailed to the registered address of such Person. Any such interest which is payable, but is not so punctually paid or duly provided for, shall forthwith cease to be payable to the registered Holder on such Regular Record Date and may be paid either to the Person in whose name this Debenture (or one or more Predecessor Securities) is registered at the close of business on a Special Record Date for the payment of such Defaulted Interest to be fixed by the Trustee, notice whereof shall be given to Holders of Debentures not less than 10 days prior to such Special Record Date, or may be paid at any time in any other lawful manner not inconsistent with the requirements of any securities exchange on which the Debentures may be listed and upon such notice as may be required by such exchange, if such manner of payment shall be deemed practical by the Trustee, all as more fully provided in the Indenture. Notwithstanding the foregoing, in the case of interest payable at Stated Maturity, such interest shall be paid to the same Person to whom the principal hereof is payable.

The Bank of New York will be the Paying Agent and the Security Registrar with respect to the Debentures. The Company reserves the right at any time to vary or terminate the appointment of any Paying Agent or Security Registrar, to appoint additional or other Paying Agents and other Security Registrars, which may include the Company, and to approve any change in the office through which any Paying Agent or Security Registrar acts; provided that there will at all times be a Paying Agent in The City of New York and there will be no more than one Security Registrar for the Debentures.

This Debenture is one of the duly authorized issue of notes, debentures, bonds or other evidences of indebtedness (hereinafter called the “Securities”) of the Company, of the series hereinafter specified, all issued or to be issued under and pursuant to the Indenture, to which Indenture and any other indentures supplemental thereto reference is hereby made for a statement of the respective rights, limitations of rights, obligations, duties and immunities thereunder of the Trustee and any agent of the Trustee, any Paying Agent, the Security Registrar, the Company and the Holders of the Securities and the terms upon which the Securities are issued and are to be authenticated and delivered.

The Securities may be issued in one or more series, which different series may be issued in various aggregate principal amounts, may mature at different times, may bear interest (if any) at different rates, may be subject to different redemption provisions (if any), may be subject to different sinking, purchase or analogous funds (if any), may be subject to different covenants and Events of Default and may otherwise vary as provided or permitted in the Indenture. This Debenture is one of the series of Securities of the Company issued pursuant to the Indenture and designated as the 6.150% Debentues due 2037 (herein called the “Debentures”).

The Debentures will be redeemable in whole or in part at any time and from time to time, at the option of the Company, at a Redemption Price equal to the greater of (i) 100% of the principal amount of the Debentures to be redeemed or (ii) the sum of the present values of the remaining scheduled payments of principal and interest thereon (exclusive of interest accrued to the Redemption Date) discounted to the Redemption Date on a semiannual basis (assuming a 360-day year consisting of twelve 30-day months) at the Treasury Rate (as defined below) plus 25 basis points, plus, in either case, accrued and unpaid interest on the principal amount being redeemed to the Redemption Date.

“Treasury Rate” means, with respect to any Redemption Date, (i) the yield, under the heading which represents the average for the immediately preceding week, appearing in the most recently published statistical release designated “H.15(519)” or any successor publication which is published weekly by the Board of Governors of the Federal Reserve System and which establishes yields on actively traded United States Treasury securities adjusted to constant maturity under the caption “Treasury Constant Maturities,” for the maturity corresponding to the Comparable Treasury Issue (if no maturity is within three months before or after the Remaining Life, yields for the two published maturities most closely corresponding to the Comparable Treasury Issue shall be determined and the Treasury Rate shall be interpolated or extrapolated from such yields on a straight line basis, rounding to the nearest month) or (ii) if such release (or any successor release) is not published during the week preceding the calculation date or does not contain such yields, the rate per annum equal to the semiannual equivalent yield to maturity of the Comparable Treasury Issue, calculated using a price for the Comparable Treasury Issue (expressed as a percentage of its principal amount) equal to the Comparable Treasury Price for such redemption date. The Treasury Rate shall be calculated on the third Business Day preceding the Redemption Date.

“Business Day” means any calendar day that is not a Saturday, Sunday or legal holiday in New York, New York and on which commercial banks are open for business in New York, New York.

“Comparable Treasury Issue” means the United States Treasury security selected by the Independent Investment Banker as having a maturity comparable to the remaining term (“Remaining Life”) of the Debentures to be redeemed that would be utilized, at the time of selection and in accordance with customary financial practice, in pricing new issues of corporate debt securities of comparable maturity to the remaining term of such Debentures.

“Comparable Treasury Price” means, with respect to a Redemption Date, the average of the Reference Treasury Dealer Quotations for such Redemption Date.

“Independent Investment Banker” means Citigroup Global Markets, Inc., Credit Suisse Securities (USA) LLC or J.P. Morgan Securities Inc, or if such firms are unwilling or unable to select the Comparable Treasury Issue, an independent investment banking institution of national standing appointed by the Company.

“Reference Treasury Dealer” means (i) Citigroup Global Markets Inc., Credit Suisse Securities (USA) LLC, J.P. Morgan Securities Inc., and their respective successors, provided, however, that if any of the foregoing is not at the time a primary U.S. Government securities dealer in New York City (a “Primary Treasury Dealer”), the Company shall substitute therefor another Primary Treasury Dealer and (ii) any other Primary Treasury Dealer selected by the Independent Investment Banker after consultation with the Company.

“Reference Treasury Dealer Quotations” means, with respect to each Reference Treasury Dealer and any Redemption Date, the average, as determined by the Independent Investment Banker, of the bid and asked prices for the Comparable Treasury Issue (expressed in each case as a percentage of its principal amount) quoted in writing to the Independent Investment Banker at 5:00 p.m., New York City time, on the third Business Day preceding such Redemption Date.

Notice of the redemption will be mailed to Holders of Debentures by first-class mail at least 30 and not more than 60 days prior to the Redemption Date. If fewer than all of the Debentures are to be redeemed, the Trustee will select, not more than 60 days prior to the Redemption Date, the particular Debentures or portions thereof for redemption from the Outstanding Debentures not previously called by such method as the Trustee deems fair and appropriate. Notwithstanding Section 1104 of the Indenture, the notice of such redemption need not set forth the Redemption Price but only the manner of calculation thereof. The Company shall give the Trustee notice of the Redemption Price promptly after the calculation thereof and the Trustee shall have no responsibility for such calculation.

If a Change of Control Repurchase Event occurs with respect to the Debentures, unless the Company has exercised its right to redeem the Debentures as described above, and notice of such redemption has been given to the Holders of the Debentures in accordance with the Indenture, the Company will be required to make an offer to each Holder of the Debentures to repurchase all or any part (in integral multiples of $1,000) of that Holder’s Debentures at a repurchase price in cash equal to 101% of the aggregate principal amount of such Debentures repurchased plus any accrued and unpaid interest on the Debentures repurchased to, but not including, the date of repurchase. Within 30 days following a Change of Control Repurchase Event or, at the Company’s option, prior to a Change of Control, but after the public announcement of the Change of Control, the Company will mail a notice to each Holder of the Debentures, with a copy to the Trustee, describing the transaction or transactions that constitute or may constitute the Change of Control Repurchase Event and offering to repurchase the Debentures on the payment date specified in the notice, which date will be no earlier than 30 days and no later than 60 days from the date such notice is mailed. The notice shall, if mailed prior to the date of consummation of the Change of Control, state that the offer to purchase is conditioned on a Change of Control Repurchase Event occurring on or prior to the payment date specified in the notice. The Company will comply with the requirements of Rule 14e-1 under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), and any other securities laws and regulations thereunder to the extent those laws and regulations are applicable in connection with the repurchase of the Debentures as a result of a Change of Control Repurchase Event. To the extent that the provisions of any securities laws or regulations conflict with the Change of Control Repurchase Event provisions of the Debentures, the Company will comply

with the applicable securities laws and regulations and will not be deemed to have breached its obligations under the Change of Control Repurchase Event provisions of the Debentures by virtue of such conflict.

On the repurchase date following a Change of Control Repurchase Event, the Company will, to the extent lawful:

(1) accept for payment all Debentures or portions of Debentures properly tendered pursuant to the Company’s offer;

(2) deposit with the Paying Agent an amount equal to the aggregate purchase price in respect of all Debentures or portions of Debentures properly tendered; and

(3) deliver or cause to be delivered to the Paying Agent the Debentures properly accepted, together with an Officers’ Certificate stating the aggregate principal amount of Debentures being purchased by the Company.

The Paying Agent will promptly mail to each Holder of Debentures properly tendered the purchase price for the Debentures, and the Trustee will promptly authenticate and mail (or cause to be transferred by book-entry) to each Holder a new Debenture equal in principal amount to any unpurchased portion of any Debentures surrendered; provided that each new Debenture will be in a principal amount of an integral multiple of $1,000.

The Company will not be required to make an offer to repurchase the Debentures upon a Change of Control Repurchase Event if a third party makes such an offer in the manner, at the times and otherwise in compliance with the requirements for an offer made by the Company and such third party purchases all Debentures properly tendered and not withdrawn under its offer.

“Below Investment Grade Ratings Event” means, with respect to the Debentures on any day within the 60-day period (which period shall be extended so long as the rating of the Debentures is under publicly announced consideration for a possible downgrade by any of the Rating Agencies) after the earlier of (1) the occurrence of a Change of Control; or (2) public notice of the occurrence of a Change of Control or the intention by the Company to effect a Change of Control, the Debentures are rated below Investment Grade by each of the Rating Agencies. Notwithstanding the foregoing, a Below Investment Grade Ratings Event otherwise arising by virtue of a particular reduction in rating shall not be deemed to have occurred in respect of a particular Change of Control (and thus shall not be deemed a Below Investment Grade Ratings Event for purposes of the definition of Change of Control Repurchase Event hereunder) if the Rating Agencies making the reduction in rating to which this definition would otherwise apply do not announce or publicly confirm or inform the Trustee in writing at its request that the reduction was the result, in whole or in part, of any event or circumstance comprised of or arising as a result of, or in respect of, the applicable Change of Control (whether or not the applicable Change of Control shall have occurred at the time of the Below Investment Grade Ratings Event).

“Change of Control” means the consummation of any transaction (including, without limitation, any merger or consolidation) the result of which is that any “person” or “group” (as those terms are used in Section 13(d)(3) of the Exchange Act), other than the Company and its subsidiaries, becomes the beneficial owner (as defined in Rules 13d-3 and 13d-5 under the Exchange Act), directly or indirectly, of more than 50% of the combined voting power of the Company’s Voting Stock or other Voting Stock into which the Company’s Voting Stock is reclassified, consolidated, exchanged or changed measured by voting power rather than number of shares.

“Change of Control Repurchase Event” means the occurrence of both a Change of Control and a Below Investment Grade Ratings Event with respect to the Debentures.

“Investment Grade” means a rating of Baa3 or better by Moody’s (or its equivalent under any successor rating categories of Moody’s); a rating of BBB- or better by S&P (or its equivalent under any successor rating categories of S&P); and the equivalent investment grade credit rating from any additional Rating Agency or Rating Agencies selected by the Company.

“Moody’s” means Moody’s Investors Service, Inc.

“Rating Agency” means (1) each of Moody’s and S&P; and (2) if either of Moody’s or S&P ceases to rate the Debentures or fails to make a rating of the Debentures publicly available for reasons outside of the Company’s control, a “nationally recognized statistical rating organization” within the meaning of Rule 15c3-1(c)(2)(vi)(F) under the Exchange Act, selected by the Company (as certified by a Board Resolution) as a replacement agency for Moody’s or S&P, or both of them, as the case may be.

“S&P” means Standard & Poor’s Ratings Services, a division of McGraw-Hill, Inc.

“Voting Stock” of any specified “person” (as that term is used in Section 13(d)(3) of the Exchange Act) as of any date means the capital stock of such person that is at the time entitled to vote generally in the election of the board of directors of such person.

If an Event of Default with respect to the Debentures shall occur and be continuing, the principal of all of the Debentures may be declared due and payable in the manner, with the effect and subject to the conditions provided in the Indenture.

The Indenture permits, with certain exceptions as therein provided, the Company and the Trustee to enter into supplemental indentures to the Indenture for the purpose of adding any provisions to or changing in any manner or eliminating any of the provisions of the Indenture or of modifying in any manner the rights of the Holders of the Securities of each series under the Indenture with the consent of the Holders of not less than a majority in principal amount of the Securities at the time Outstanding of each series to be affected thereby on behalf of the Holders of all Securities of such series. The Indenture also permits the Holders of a majority in principal amount of the Securities at the time Outstanding of each series, on behalf of the Holders of all

Securities of such series, to waive compliance by the Company with certain provisions of the Indenture and certain past defaults and their consequences with respect to such series under the Indenture. Any such consent or waiver by the Holder of this Debenture shall be conclusive and binding upon such Holder and upon all future Holders of this Debenture and of any Debenture issued upon the registration of transfer hereof or in exchange hereof or in lieu hereof, whether or not notation of such consent or waiver is made upon this Debenture or such other Debentures.

No reference herein to the Indenture and no provision of this Debenture or of the Indenture shall alter or impair the obligation of the Company, which is absolute and unconditional, to pay the principal of and interest on this Debenture at the place, rate and respective times and in the coin or currency herein and in the Indenture prescribed.

As provided in the Indenture and subject to the satisfaction of certain conditions therein set forth, including the deposit of certain trust funds in trust, the Company shall be deemed to have paid and discharged the entire indebtedness represented by, and the obligations under, the Securities of any series and to have satisfied all the obligations (with certain exceptions) under the Indenture relating to the Securities of such series.

The Debentures are issuable in registered form without coupons in denominations of $1,000 and any integral multiple of $1,000. Debentures may be exchanged for a like aggregate principal amount of Debentures of other authorized denominations at the office or agency of the Company in the Borough of Manhattan, The City of New York, designated for such purpose, and in the manner and subject to the limitations provided in the Indenture.

Upon due presentment for registration of transfer of this Debenture at the office or agency of the Company in the Borough of Manhattan, The City of New York designated for such purpose, a new Debenture or Debentures of authorized denominations for a like aggregate principal amount will be issued to the transferee in exchange therefor, subject to the limitations provided in the Indenture.

No charge shall be made for any such transfer or exchange, but the Company may require payment of a sum sufficient to cover any tax or other governmental charge imposed in connection therewith.

Except as otherwise provided in the Indenture, the Company, the Trustee and any agent of the Company or the Trustee may treat the Person in whose name this Debenture is registered as the owner hereof for all purposes, whether or not this Debenture is overdue, and neither the Company, the Trustee nor any such agent shall be affected by notice to the contrary.

Unless otherwise defined herein, all terms used in this Debenture which are defined in the Indenture shall have the meanings assigned to them in the Indenture.

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

Unless the certificate of authentication hereon has been manually executed by or on behalf of the Trustee under the Indenture, this Debenture shall not be entitled to any benefits under the Indenture, or be valid or obligatory for any purpose.

IN WITNESS WHEREOF, UNION PACIFIC CORPORATION has caused this Debenture to be duly executed.

TRUSTEE’S CERTIFICATE OF AUTHENTICATION

This is one of the Securities of the series designated therein referred to in the within mentioned Indenture.