SC TO-T/A

UNITED STATES SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE TO

Tender Offer Statement under Section 14(d)(1) or 13(e)(1)

of the Securities Exchange Act of 1934

(Amendment No. 3)

BRONCO DRILLING COMPANY, INC.

(Name of Subject Company)

NOMAC ACQUISITION, INC.

CHESAPEAKE ENERGY CORPORATION

(Names of Filing Persons — Offeror)

Common Stock, Par Value $0.01 Per Share

(Title of Class of Securities)

112211107

(Cusip Number of Class of Securities)

Jennifer M. Grigsby

Senior Vice President, Treasurer and

Corporate Secretary

6100 North Western Avenue

Oklahoma City, Oklahoma 73118

Telephone: (405) 848-8000

(Name, Address and Telephone Number of Person Authorized to Receive Notices

and Communications on Behalf of Filing Persons)

Copies to:

Ray Lees, Esq. Commercial Law Group, P.C. 5520 North Francis Avenue Oklahoma City, Oklahoma 73118 Telephone: (405) 232-3001 David A. Katz, Esq. Wachtell, Lipton, Rosen & Katz 51 West 52nd Street New York, New York 10019 Telephone: (212) 403-1000

CALCULATION OF FILING FEE

Transaction Valuation*	Amount of Filing Fee**
$376,649,119	$43,728.96

* Estimated for purposes of calculating the filing fee only. This amount is based on the offer to purchase at a purchase price of $11.00 cash per share (i) all 28,800,059 shares of common stock of the subject company, which represents all outstanding shares of common stock of the subject company, other than those shares held by Bronco Drilling Company, Inc., Chesapeake Energy Corporation, Nomac Acquisition, Inc. and their wholly owned subsidiaries, as of April 13, 2011, the most practicable date before filing, and (ii) if issued, all 5,440,770 shares of common stock of the subject company that would be issuable upon conversion of the warrant of the subject company that is currently outstanding.

** The amount of the filing fee is calculated in accordance with Section 13(e) of the Securities Exchange Act of 1934, as amended, and Fee Rate Advisory #5 for the fiscal year 2011, issued December 22, 2010, by multiplying the transaction valuation by 0.00011610.

x Check box if any part of the fee is offset as provided by Rule 0-11(a)(2) and identify the filing with which the offsetting fee was previously paid. Identify the previous filing by registration statement number, or the Form or Schedule and the date of its filing.

Amount Previously Paid:	$43,728.96	Filing Party:	Nomac Acquisition, Inc. and Chesapeake Energy Corporation
Form or Registration No.:	Schedule TO	Date Filed:	April 26, 2011

¨ Check the box if the filing relates solely to preliminary communications made before the commencement of a tender offer.

Check the appropriate boxes below to designate any transactions to which the statement relates:

x third-party tender offer subject to Rule 14d-1.

¨ issuer tender offer subject to Rule 13e-4.

¨ going-private transaction subject to Rule 13e-3.

¨ amendment to Schedule 13D under Rule 13d-2.

Check the following box if the filing is a final amendment reporting the results of the tender offer.  ¨

This Amendment No. 3 (this “Amendment No. 3”) amends and supplements the Tender Offer Statement on Schedule TO (together with any amendments and supplements thereto, the “Schedule TO”) filed with the Securities and Exchange Commission (the “SEC”) on April 26, 2011, as amended by the Amendment No. 1 to the Schedule TO filed on May 3, 2011 and by the Amendment No. 2 to the Schedule TO filed on May 5, 2011, and is filed by (i) Nomac Acquisition, Inc., a Delaware corporation (“Purchaser”) and an indirect wholly owned subsidiary of Chesapeake Energy Corporation, an Oklahoma corporation (“Chesapeake”), and (ii) Chesapeake. The Schedule TO relates to the tender offer by Purchaser and Chesapeake to purchase all outstanding shares of common stock, par value $0.01 per share (the “Bronco shares”), of Bronco Drilling Company, Inc., a Delaware corporation (“Bronco”), at $11.00 per share in cash, without interest, upon the terms and subject to the conditions set forth in the Offer to Purchase, dated April 26, 2011 (the “Offer to Purchase”), and in the related Letter of Transmittal, copies of which were filed with the Schedule TO as Exhibits (a)(1)(A) and (a)(1)(B), respectively (which, together with any amendments or supplements, collectively constitute the “offer”). The offer is made pursuant to the Agreement and Plan of Merger, dated as of April 14, 2011 and amended as of May 17, 2011 (the “merger agreement”), by and among Chesapeake, Purchaser and Bronco.

The information in the Offer to Purchase and the related Letter of Transmittal is incorporated in this Amendment No. 3 by reference to all of the applicable items in the Schedule TO, except that such information is amended and supplemented to the extent specifically provided in this Amendment No. 3. Capitalized terms used and not otherwise defined in this Amendment No. 3 shall have the meanings assigned to such terms in the Offer to Purchase or in the Schedule TO.

Items 1 through 11. Summary Term Sheet; Subject Company Information; Identity and Background of Filing Person; Terms of the Transaction; Past Contacts, Transactions, Negotiations and Agreements; Purposes of the Transaction and Plans or Proposals; Source and Amount of Funds or Other Consideration; Interest in Securities of the Subject Company; Persons/Assets Retained, Employed, Compensated or Used; Financial Statements; Additional Information.

1. The information under the sub-heading “—Legal Proceedings” in Section 15 – “Certain Legal Matters; Regulatory Approvals” on page 41 of the Offer to Purchase in the section entitled “The Offer” is hereby amended and restated as follows:

Ten putative class action lawsuits relating to the merger agreement and the transactions contemplated therein have been commenced against Bronco and current members of the Bronco Board, including Bronco’s chief executive officer (the “Individual Defendants”). Six putative class action lawsuits were filed in the District Court of Oklahoma County, Oklahoma (collectively, the “Oklahoma Suits”). All but one of the Oklahoma Suits have been voluntarily dismissed. Four putative class action lawsuits were filed in the Court of Chancery of the State of Delaware (the “Delaware Suits” and together with the one remaining Oklahoma Suit, the “Class Actions”). The Class Actions each seek certification of a class of all holders of Bronco’s common stock and variously allege, among other things, that: (1) the Individual Defendants have breached and continue to breach their fiduciary duties to the stockholders of Bronco; (2) the offer and the merger are unfair to the public stockholders of Bronco as the proposed transactions underestimate the value of Bronco; (3) the Individual Defendants are pursuing a course of conduct that does not maximize the value of Bronco; and (4) Bronco aided and abetted the alleged breaches of duties by the Individual Defendants. The Delaware Suits also name Chesapeake and Purchaser as defendants, in each case alleging that Chesapeake and Purchaser aided and abetted the alleged breaches of duties by the Individual Defendants. On April 29, 2011, one of the Delaware Suits was amended, adding allegations that Bronco’s 14D-9 and Chesapeake’s Schedule TO did not adequately describe the process that resulted in the offer and that Bronco’s 14D-9 did not include adequate information concerning the fairness opinion Johnson Rice & Company L.L.C. provided to the Bronco Board. The Delaware Suits were consolidated into a single action on May 6, 2011. On May 10, 2011, the Oklahoma Suit was stayed in favor of the Delaware Suits. The Class Actions seek, among other things, an injunction prohibiting consummation of the tender offer and the merger, attorneys’ fees and expenses and rescission or damages in the event the proposed transactions are consummated. A preliminary injunction hearing has been scheduled in the Delaware Suits for May 19, 2011. We believe the Class Actions are entirely without merit.

2

On May 17, 2011, the parties to the Delaware Suits informed the Court of Chancery that they had reached an agreement in principle, which, if approved by the Court, would result in the settlement of all claims brought on behalf of the purported class. Pursuant to that agreement: (i) Chesapeake, Bronco and Purchaser have agreed to amend the merger agreement to shorten from twelve (12) months to nine (9) months the period during which, if Bronco enters into a definitive Contract to consummate, or consummates any transaction contemplated by any Takeover Proposal, Bronco must pay Chesapeake the Termination Fee (as those terms are defined in the merger agreement); (ii) Bronco will make additional disclosures in an amendment to its Schedule 14D-9; and (iii) Chesapeake and Purchaser will extend the expiration of the offer from 12:00 midnight New York City time at the end of Monday, May 23, 2011 to 12:00 midnight New York City time at the end of Tuesday, May 31, 2011. The parties have entered into a memorandum of understanding memorializing the key terms of that agreement. The memorandum of understanding is attached as Exhibit a(5)(Q) hereto and is incorporated by reference.

The Individual Defendants, Bronco, Chesapeake and Purchaser have denied, and continue to deny, that they have committed or aided and abetted in the commission of any violation of law or engaged in any of the alleged wrongful acts, and expressly maintain that they diligently and scrupulously complied with their fiduciary and other legal duties.

2. The following information in Section 11 – “Background of the Offer” of the Offer to Purchase in the section entitled “The Offer” is hereby amended as follows:

(a) the second paragraph in Section 11 – “Background of the Offer” on page 17 of the Offer to Purchase in the section entitled “The Offer” is hereby amended and restated as follows:

On October 27, 2010, a representative of Jefferies & Company, Inc. (“Jefferies”) contacted Zachary M. Graves, Bronco’s Executive Vice President of Operations. Among other topics, the Jefferies representative suggested that Chesapeake was interested in growing its service assets as part of its ongoing vertical integration strategy and to meet drilling commitments and growth targets. In the event that Chesapeake was interested in acquiring Bronco, Mr. Graves and the representative of Jefferies discussed that because of Chesapeake’s vertical integration strategy, it might result in a superior offer than could be obtained from another service company or financial buyer. At the time, Jefferies was not engaged on behalf of Bronco or Chesapeake.

(b) the third paragraph in Section 11 – “Background of the Offer” on page 17 of the Offer to Purchase in the section entitled “The Offer” is hereby amended and restated as follows:

On October 29, 2010, a representative of Jefferies called Mr. Graves to confirm that Chesapeake was interested in discussing a potential acquisition of Bronco. At the time, Jefferies was not engaged on behalf of Bronco or Chesapeake.

(c) the seventh paragraph in Section 11 – “Background of the Offer” on page 17 of the Offer to Purchase in the section entitled “The Offer” is hereby amended and restated as follows:

On November 10, 2010, Aubrey K. McClendon, Chesapeake’s Chairman of the Board of Directors and Chief Executive Officer, Domenic J. Dell’Osso, Jr., Chesapeake’s Chief Financial Officer, and other representatives of Chesapeake’s management met with Messrs. Harrison, Graves, Dubberstein and Porter of Bronco, together with Jefferies, at which meeting they discussed Bronco’s business, rig fleet and initiatives to reduce its indebtedness, including Bronco’s ongoing strategic divestiture of some of its drilling rigs that were not suited to horizontal drilling in domestic shale plays. At the meeting, discussions ensued regarding additional financial and operational information concerning Bronco’s drilling rigs that Chesapeake would require before it could establish a value for Bronco.

(d) the eighteenth paragraph in Section 11 – “Background of the Offer” on page 18 of the Offer to Purchase in the section entitled “The Offer” is hereby amended and restated as follows:

From March 31, 2011 through April 11, 2011, Jefferies requested from Johnson Rice certain additional financial and operating data for Bronco, including, among other things, drilling rig status reports, drilling rig contract data, the February 2011 balance sheet and information relating to Bronco’s joint ventures in Mexico and Libya, which data was supplied by Johnson Rice and Bronco’s management.

(e) the first sentence of the nineteenth paragraph in Section 11 – “Background of the Offer” on page 18 of the Offer to Purchase in the section entitled “The Offer” is hereby amended and restated as follows:

On April 4, 2011, Mr. McClendon sent a letter to Mr. Harrison indicating that Chesapeake remained interested in a potential acquisition of Bronco and that, based upon the increase in Bronco’s share price since Chesapeake’s initial proposal, it had revisited its valuation metrics and was prepared to offer $11.00 per share in cash, representing an approximately 2.8% discount to the previous day’s close of $11.32 per share, a 14% premium to the thirty day average market price of Bronco shares and a 45% premium to the ninety day average price.

3

The letter indicated that the proposal was subject only to the completion of customary due diligence and the negotiation and execution of mutually acceptable definitive documentation.

3. The second paragraph under the sub-heading “— Effect of Termination; Termination Fee” in Section 12 – “Purpose of the Offer; Plans for Bronco; The Merger Agreement; The Tender Support Agreements; Appraisal Rights; Going Private Transactions” on page 33 of the Offer to Purchase in the section entitled “The Offer” is hereby amended and restated as follows:

If:

• the merger agreement is terminated pursuant to clause 3(B) or 4(B) described under “— Termination”; or

• a Takeover Proposal is made or publically announced, thereafter the merger agreement is terminated by Bronco pursuant to clause 2(A) or by either Bronco or Chesapeake pursuant to clause 2(C), in each case, as described under “— Termination” above, and within 9 months after such termination, Bronco enters into a definitive contract to consummate, or consummates, the transactions contemplated by any Takeover Proposal,

then Bronco will pay Chesapeake a termination fee equal to $13,000,000, plus expenses (without duplication if paid under any other provision of the merger agreement) of up to $1,500,000.

4. The information set forth in the sections of the Offer to Purchase entitled “Summary Term Sheet,” “Questions and Answers Relating to the Offer” and “Introduction” and in Section 1 — “Terms of the Offer” of the Offer to Purchase in the section entitled “The Offer” is hereby amended and supplemented as follows:

On May 18, 2011, Chesapeake and Purchaser announced that the expiration of the Offer was extended until 12:00 Midnight, New York City time, at the end of Tuesday, May 31, 2011. Accordingly, the term “Expiration Date” means 12:00 Midnight, New York City time, at the end of Tuesday, May 31, 2011, unless further extended, in which event “expiration date” means the latest time and date at which the offer, as so extended, will expire. A copy of the press release announcing the extension of the Offer is attached hereto as Exhibit (a)(5)(P) and is incorporated by reference.

5. The information set forth in the Schedule TO and Offer to Purchase is hereby amended and supplemented as follows:

All references to the Agreement and Plan of Merger, dated as of April 14, 2011, by and among Chesapeake Energy Corporation, Nomac Acquisition, Inc. and Bronco Drilling Company, Inc. are hereby deemed to be references to the Agreement and Plan of Merger, dated as of April 14, 2011 and amended as of May 17, 2011, by and among Chesapeake Energy Corporation, Nomac Acquisition, Inc. and Bronco Drilling Company, Inc.

Item 12. Exhibits.

Item 12 of the Schedule TO is hereby amended and supplemented by adding the following exhibits:

“(a)(5)(P)	Joint Press Release issued by Chesapeake Energy Corporation and Bronco Drilling Company, Inc. on May 18, 2011.”
“(a)(5)(Q)	Memorandum of Understanding, dated as of May 17, 2011 (incorporated by reference to Exhibit (a)(5)(O) to the Solicitation/Recommendation Statement on Schedule 14D-9 filed by Bronco Drilling Company, Inc. with the SEC on May 18, 2011).”
“(d)(4)	Amendment No. 1, dated as of May 17, 2011, to the Agreement and Plan of Merger, dated as of April 14, 2011, by and among Chesapeake Energy Corporation, Nomac Acquisition, Inc. and Bronco Drilling Company, Inc.”

4

SIGNATURES

After due inquiry and to the best knowledge and belief of the undersigned, each of the undersigned certify that the information set forth in this statement is true, complete and correct.

Dated: May 18, 2011

NOMAC ACQUISITION, INC.
By:	/s/ Domenic J. Dell’Osso, Jr.
	Name:	Domenic J. Dell’Osso, Jr.
	Title:	Executive Vice President and Chief Financial Officer

CHESAPEAKE ENERGY CORPORATION
By:	/s/ Domenic J. Dell’Osso, Jr.
	Name:	Domenic J. Dell’Osso, Jr.
	Title:	Executive Vice President and Chief Financial Officer

5

EXHIBIT INDEX

Exhibit No.	Description
(a)(1)(A)	Offer to Purchase dated April 26, 2011.*
(a)(1)(B)	Form of Letter of Transmittal (including Internal Revenue Service Form W-9).*
(a)(1)(C)	Form of Notice of Guaranteed Delivery.*
(a)(1)(D)	Form of Letter to Brokers, Dealers, Commercial Banks, Trust Companies and Other Nominees.*
(a)(1)(E)	Form of Letter to Clients for use by Brokers, Dealers, Commercial Banks, Trust Companies and Other Nominees.*
(a)(2)	None.
(a)(3)	None.
(a)(4)	None.
(a)(5)(A)	Form of Summary Advertisement Published in The Wall Street Journal on April 26, 2011.*
(a)(5)(B)	Press release issued by Chesapeake Energy Corporation on April 26, 2011 announcing commencement of the tender offer.*
(a)(5)(C)	Petition filed on April 18, 2011 in the District Court of Oklahoma County: State of Oklahoma, captioned Sanjay Israni, on behalf of himself and all others similarly situated v. Bronco Drilling Company, Inc., D. Frank Harrison, Richard B. Hefner, David W. House, William R. Snipes, Gary C. Hill, and Chesapeake Energy Corporation (Case No. CJ-2011-2601) (incorporated by reference to Exhibit (a)(5)(B) to the Solicitation/Recommendation Statement on Schedule 14D-9 filed by Bronco Drilling Company, Inc. with the SEC on April 26, 2011).*
(a)(5)(D)	Petition filed on April 19, 2011 in the District Court of Oklahoma County: State of Oklahoma, captioned Frank Kramer, on behalf of himself and all others similarly situated v. Bronco Drilling Company, Inc., D. Frank Harrison, Richard B. Hefner, Gary C. Hill, David W. House, William R. Snipes, and Chesapeake Energy Corporation (Case No. CJ-2011-2627) (incorporated by reference to Exhibit (a)(5)(C) to the Solicitation/Recommendation Statement on Schedule 14D-9 filed by Bronco Drilling Company, Inc. with the SEC on April 26, 2011).*
(a)(5)(E)	Complaint filed on April 20, 2011 in the Court of Chancery of the State of Delaware: State of Delaware, captioned Sam Berlinberg v. Bronco Drilling Company, Inc., Chesapeake Energy Corporation, Nomac Acquisition, Inc., D. Frank Harrison, Richard B. Hefner, David W. House, William R. Snipes, and Gary C. Hill (Case No. 6398) (incorporated by reference to Exhibit (a)(5)(D) to the Solicitation/Recommendation Statement on Schedule 14D-9 filed by Bronco Drilling Company, Inc. with the SEC on April 26, 2011).*
(a)(5)(F)	Petition filed on April 20, 2011 in the District Court of Oklahoma County: State of Oklahoma, captioned Daniel B. Leader, on behalf of himself and all others similarly situated v. Bronco Drilling Company, Inc., D. Frank Harrison, William R. Snipes, Gary C. Hill, David W. House, and Richard B. Hefner (Case No. CJ-2011-2684) (incorporated by reference to Exhibit (a)(5)(E) to the Solicitation/Recommendation Statement on Schedule 14D-9 filed by Bronco Drilling Company, Inc. with the SEC on April 26, 2011).*
(a)(5)(G)	Petition filed on April 20, 2011 in the District Court of Oklahoma County: State of Oklahoma, captioned Debra Kushner, individually and on behalf of all others similarly situated v. Bronco Drilling Company, Inc., D. Frank Harrison, Richard B. Hefner, David W. House, Gary C. Hill, and William R. Snipes (Case No. CJ-2011-2687) (incorporated by reference to Exhibit (a)(5)(F) to the Solicitation/Recommendation Statement on Schedule 14D-9 filed by Bronco Drilling Company, Inc. with the SEC on April 26, 2011).*

(a)(5)(H)	Petition filed on April 21, 2011 in the District Court of Oklahoma County: State of Oklahoma, captioned Barr Shriver, individually and on behalf of all others similarly situated v. Bronco Drilling Company, Inc., D. Frank Harrison, Richard B. Hefner, David W. House, Gary C. Hill, and William R. Snipes (Case No. CJ-2011-2723) (incorporated by reference to Exhibit (a)(5)(G) to the Solicitation/Recommendation Statement on Schedule 14D-9 filed by Bronco Drilling Company, Inc. with the SEC on April 26, 2011).*
(a)(5)(I)	Petition filed on April 22, 2011 in the District Court of Oklahoma County: State of Oklahoma, captioned Ralph C. Brand, individually and on behalf of all others similarly situated v. D. Frank Harrison, William Snipes, Gary Hill, David House, Richard Hefner, Bronco Drilling Company, Inc., Chesapeake Energy Corporation, and Nomac Acquisition, Inc. (Case No. CJ-2011-2738) (incorporated by reference to Exhibit (a)(5)(H) to the Solicitation/Recommendation Statement on Schedule 14D-9 filed by Bronco Drilling Company, Inc. with the SEC on April 26, 2011).*
(a)(5)(J)	Press release dated April 15, 2011 (incorporated by reference to the Schedule TO filed by Chesapeake Energy Corporation with the SEC on April 15, 2011).*
(a)(5)(K)	Complaint filed on April 26, 2011 in the Court of Chancery of the State of Delaware: State of Delaware, captioned Theodore Dass, individually and on behalf of all others similarly situated v. Bronco Drilling Company, Inc., D. Frank Harrison, David W. House, Richard B. Hefner, Gary C. Hill, William R. Snipes, Chesapeake Energy Corporation, and Nomac Acquisition, Inc. (Case No. 6419) (incorporated by reference to Exhibit (a)(5)(I) to the Solicitation/Recommendation Statement on Schedule 14D-9 filed by Bronco Drilling Company, Inc. with the SEC on May 3, 2011).*
(a)(5)(L)	Plaintiffs’ Notice of Dismissal Without Prejudice in the District Court of Oklahoma County: State of Oklahoma, captioned Frank Kramer, on behalf of himself and all others similarly situated v. Bronco Drilling Company, Inc., D. Frank Harrison, Richard B. Hefner, Gary C. Hill, David W. House, William R. Snipes, and Chesapeake Energy Corporation (Case No. CJ-2011-2627) (incorporated by reference to Exhibit (a)(5)(J) to the Solicitation/Recommendation Statement on Schedule 14D-9 filed by Bronco Drilling Company, Inc. with the SEC on May 3, 2011).*
(a)(5)(M)	Complaint filed on April 28, 2011 in the Court of Chancery of the State of Delaware: State of Delaware, captioned Charles Miller, on behalf of himself and all others similarly situated v. Bronco Drilling Company, Inc., D. Frank Harrison, Richard B. Hefner, Gary C. Hill, David W. House, William R. Snipes, Chesapeake Energy Corporation, and Nomac Acquisition, Inc. (Case No. 6434) (incorporated by reference to Exhibit (a)(5)(K) to the Solicitation/Recommendation Statement on Schedule 14D-9 filed by Bronco Drilling Company, Inc. with the SEC on May 3, 2011).*
(a)(5)(N)	Amended Complaint filed on April 29, 2011 in the Court of Chancery of the State of Delaware: State of Delaware, captioned Sam Berlinberg, on behalf of himself and all others similarly situated v. Bronco Drilling Company, Inc., Chesapeake Energy Corporation, Nomac Acquisition, Inc., D. Frank Harrison, Richard B. Hefner, David W. House, William R. Snipes, and Gary C. Hill (Case No. 6398-VCP) (incorporated by reference to Exhibit (a)(5)(L) to the Solicitation/Recommendation Statement on Schedule 14D-9 filed by Bronco Drilling Company, Inc. with the SEC on May 3, 2011).*
(a)(5)(O)	Complaint filed on April 29, 2011 in the Court of Chancery of the State of Delaware: State of Delaware, captioned Eillis Toews, individually and on behalf of all others similarly situated v. D. Frank Harrison, Richard B. Hefner, David W. House, Gary C. Hill, William R. Snipes, Bronco Drilling Company, Inc., Chesapeake Energy Corporation, and Nomac Acquisition, Inc. (Case No. 6432) (incorporated by reference to Exhibit (a)(5)(M) to the Solicitation/Recommendation Statement on Schedule 14D-9 filed by Bronco Drilling Company, Inc. with the SEC on May 3, 2011).*
(a)(5)(P)	Joint Press Release issued by Chesapeake Energy Corporation and Bronco Drilling Company, Inc. on May 18, 2011.**
(a)(5)(Q)	Memorandum of Understanding, dated as of May 17, 2011 (incorporated by reference to Exhibit (a)(5)(O) to the Solicitation/Recommendation Statement on Schedule 14D-9 filed by Bronco Drilling Company, Inc. with the SEC on May 18, 2011).**
(b)	None.
(d)(1)	Agreement and Plan of Merger, dated as of April 14, 2011, by and among Chesapeake Energy Corporation, Nomac Acquisition, Inc. and Bronco Drilling Company, Inc. (incorporated by reference to Exhibit 2 to the Schedule 13D filed by Chesapeake Energy Corporation with the SEC on April 25, 2011).*

(d)(2)	Tender Support Agreement, dated as of April 14, 2011, by and among Chesapeake Energy Corporation, Nomac Acquisition, Inc., Inmobiliaria Carso, S.A. de C.V. and Carso Infraestructura y Construcción, S.A.B. de C.V. (incorporated by reference to Exhibit 3 to the Schedule 13D filed by Chesapeake Energy Corporation with the SEC on April 25, 2011).*
(d)(3)	Tender Support Agreement, dated as of April 14, 2011, by and among Chesapeake Energy Corporation, Nomac Acquisition, Inc. and Third Avenue Management LLC (incorporated by reference to Exhibit 4 to the Schedule TO filed by Chesapeake Energy Corporation with the SEC on April 25, 2011).*
(d)(4)	Amendment No. 1, dated as of May 17, 2011, to the Agreement and Plan of Merger, dated as of April 14, 2011, by and among Chesapeake Energy Corporation, Nomac Acquisition, Inc. and Bronco Drilling Company, Inc.**
(g)	None.
(h)	None.

* Previously filed.

** Filed herewith.

EX-99.(A)(5)(P)

Exhibit a(5)(P)

News Release

    

FOR IMMEDIATE RELEASE

MAY 18, 2011

CHESAPEAKE ENERGY CORPORATION AND BRONCO DRILLING

COMPANY, INC. ANNOUNCE ENTRY INTO A MEMORANDUM OF UNDERSTANDING IN

SHAREHOLDER LAWSUIT

Tender Offer for Bronco Shares Extended Through May 31, 2011

OKLAHOMA CITY, OKLAHOMA, MAY 18, 2011 – Chesapeake Energy Corporation (NYSE:CHK) and Bronco Drilling Company, Inc. (NASDAQ: BRNC) today announced that they have entered into a memorandum of understanding on May 17, 2011 as to the key terms of the settlement agreement in connection with the putative consolidated class action, captioned In Re: Bronco Drilling Company, Inc. Shareholder Litigation (Consolidated C.A. No. 6398-VCP), pending in the Court of Chancery of the State of Delaware.

Pursuant to the memorandum of understanding, Chesapeake and Bronco have entered into an amendment to the pending merger agreement and Nomac Acquisition, Inc., Chesapeake’s indirect wholly owned subsidiary, has extended its cash tender offer to purchase all outstanding shares of common stock of Bronco. The cash tender offer was previously scheduled to expire at 12:00 midnight, New York City time, on Monday, May 23, 2011 and will now expire at 12:00 midnight, New York City time, on Tuesday, May 31, 2011, unless further extended in accordance with the merger agreement, applicable rules and regulations and the procedures described in the Offer to Purchase. Pursuant to the cash tender offer, Nomac Acquisition, Inc. is offering to purchase all outstanding Bronco shares for $11.00 per share in cash, without interest and less any required withholding taxes.

The extension of the tender offer will afford Bronco stockholders additional time to receive and consider supplemental disclosures in the Schedule 14D-9 filed by Bronco today in connection with the memorandum of understanding. Accordingly, unless further extended, the tender offer and withdrawal rights will expire at 12:00 midnight, New York City time, at the end of the day on Tuesday, May 31, 2011. The tender offer remains subject to satisfaction of other customary closing conditions described in the Offer to Purchase.

The complete terms and conditions of the tender offer are set forth in the Offer to Purchase and related Letter of Transmittal that have been sent to holders of Bronco common stock. Copies of the Offer to Purchase and Letter of Transmittal may be obtained at no charge from the information agent, MacKenzie Partners, Inc., by calling (800) 322-2885 (toll-free) or (212) 929-5500 (collect). Additionally, any questions related to the tender offer may be directed to MacKenzie Partners, Inc. at the telephone numbers provided above.

Johnson Rice & Company L.L.C. is acting as financial advisor to Bronco. Thompson & Knight LLP and Richards, Layton and Finger P.A. are acting as legal advisors to Bronco. Jefferies & Company, Inc. is acting as financial advisor to Chesapeake. Commercial Law Group, P.C. and Wachtell, Lipton, Rosen & Katz are acting as legal advisors to Chesapeake.

About Chesapeake:

Chesapeake Energy Corporation is the second-largest producer of natural gas, a Top 15 producer of oil and natural gas liquids and the most active driller of new wells in the U.S. Headquartered in Oklahoma City, the company’s operations are focused on discovering and developing unconventional natural gas and oil fields onshore in the U.S. Chesapeake owns leading positions in the Barnett, Haynesville, Bossier, Marcellus and Pearsall natural gas shale plays and in the Granite Wash, Cleveland, Tonkawa, Mississippian, Bone Spring, Avalon, Wolfcamp, Wolfberry, Eagle Ford, Niobrara, Three Forks/Bakken and Utica unconventional liquids plays. The company has also vertically integrated its operations and owns substantial midstream, compression, drilling and oilfield service assets. Chesapeake’s stock is listed on the New York Stock Exchange under the symbol CHK. Further information is available at www.chk.com where Chesapeake routinely posts announcements, updates, events, investor information, presentations and press releases.

About Bronco:

Bronco Drilling Company, Inc. is a publicly held company headquartered in Edmond, Oklahoma, and is a provider of contract land drilling to oil and natural gas exploration and production companies. Bronco’s common stock is quoted on The NASDAQ Global Select Market under the symbol “BRNC”. For more information about Bronco Drilling Company, Inc., visit http://www.broncodrill.com.

Important Information:

This press release is neither an offer to purchase nor a solicitation of an offer to sell securities. Chesapeake filed a tender offer statement with the SEC on April 26, 2011 (which was amended by amendments filed with the SEC on May 3, 2011, May 5, 2011 and May 17, 2011), and has mailed an offer to purchase, forms of letter of transmittal and related documents to Bronco stockholders. Bronco has filed with the SEC on April 26, 2011 (which was amended by amendments filed with the SEC on May 3, 2011 and May 17, 2011), and has mailed to Bronco stockholders, a solicitation/recommendation statement on Schedule 14D-9. INVESTORS AND BRONCO STOCKHOLDERS ARE STRONGLY ADVISED TO READ THE TENDER OFFER STATEMENT (INCLUDING THE OFFER TO PURCHASE, LETTER OF TRANSMITTAL AND RELATED TENDER OFFER DOCUMENTS) AND THE RELATED SOLICITATION/RECOMMENDATION STATEMENT ON SCHEDULE 14D-9 BECAUSE THEY CONTAIN IMPORTANT INFORMATION.

The offer to purchase, the related letter of transmittal and certain other offer documents, as well as the solicitation/recommendation statement, have been and will be made available to all shareholders of Bronco at no expense to them. These documents are also be available at no charge from the SEC’s website at www.sec.gov. Free copies of these documents may also be obtained from the Information Agent by contacting the MacKenzie Partners, Inc. at 105 Madison Avenue, New York, NY 10016, or by calling (212) 929-5500 (collect) or (800) 322-2885 (toll-free). In addition, investors and Bronco shareholders may obtain a free copy of these documents from Bronco by contacting Bronco Drilling Company, Inc. at 16217 N. May Ave., Edmond, OK 73013, attention: Investor Relations.

Forward Looking Statements:

This press release contains, among other things, certain statements of a forward-looking nature. Such statements include all statements other than those made solely with respect to historical fact. Numerous risks, uncertainties and other factors may cause actual results to differ materially from those expressed in any forward-looking statement. These factors include, but are not limited to, (1) the occurrence of any event, change or other circumstance that could give rise to the termination of the definitive agreement; (2) successful completion of the proposed transaction on a timely basis; (3) the impact of regulatory reviews on the proposed transaction; (4) the outcome of any legal proceedings that may be instituted against Chesapeake and others following the announcement of the definitive agreement; (5) risks that the proposed transaction disrupts current plans and operations and the potential difficulties in employee retention as a result of the transaction; and (6) other factors described in Chesapeake’s filings with the SEC, including its reports on Forms 10-K, 10-Q, and 8-K.

Many of the factors that will determine the outcome of the subject matter of this communication are beyond Chesapeake’s ability to control or predict. Except to the extent required by applicable law, Chesapeake does not undertake any obligation to revise or update any forward-looking statements, or to make any other forward-looking statements, whether as a result of new information, future results or otherwise.

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EX-99.(D)(4)

Exhibit (d)(4)

AMENDMENT NO. 1

TO THE

AGREEMENT AND PLAN OF MERGER

This AMENDMENT NO. 1 (this “Amendment”), dated as of May 17, 2011, to the Agreement and Plan of Merger, dated as of April 14, 2011 (the “Merger Agreement”), by and among Chesapeake Energy Corporation, an Oklahoma corporation (“Parent”), Nomac Acquisition, Inc., a Delaware corporation and a wholly owned Subsidiary of Parent (“Merger Sub”) and Bronco Drilling Company, Inc., a Delaware corporation (the “Company”).

WHEREAS, in connection with that certain memorandum of understanding entered into on May 17, 2011 by the parties to the putative consolidated class action, captioned In Re: Bronco Drilling Company, Inc. Shareholder Litigation (Consolidated C.A. No. 6398-VCP), filed in the Court of Chancery of the State of Delaware, among other things, (i) Parent, Merger Sub and the Company have agreed to amend the Merger Agreement to shorten from twelve (12) months to nine (9) months the period during which, if the Company enters into a definitive Contract to consummate, or consummates any transaction contemplated by any Takeover Proposal, Bronco must pay Chesapeake the Termination Fee; and (ii) Parent and Purchaser have agreed to extend the Expiration Date from 12:00 midnight New York City time at the end of Monday, May 23, 2011 to 12:00 midnight New York City time at the end of Tuesday, May 31, 2011;

WHEREAS, Section 7.03 of the Merger Agreement provides for the amendment of the Merger Agreement in accordance with the terms set forth therein; and

WHEREAS, the Company desires to grant a consent to the extension of the Expiration Date and the parties hereto desire to amend the Merger Agreement, in each case, as set forth herein.

NOW, THEREFORE, in consideration of the representations, warranties, covenants and agreements contained in this Agreement, and subject to the conditions set forth herein, the parties hereto agree as follows:

ARTICLE I

DEFINITIONS

Section 1.1 Definitions; References. Unless otherwise specifically defined herein, each term used herein, including the recitals hereto, shall have the meaning assigned to such term in the Merger Agreement as amended by this Amendment. Each reference in the Merger Agreement to “hereof,” “herein,” “hereunder,” “hereby” and “this Agreement” shall, from and after the date hereof, refer to the Merger Agreement as amended by this Amendment except that references to “the date hereof” and to “the date of this Agreement” shall remain references to the date of the original Merger Agreement.

ARTICLE II

CONSENT PURSUANT TO, AND AMENDMENTS TO, THE MERGER AGREEMENT

Section 2.1 Consent Pursuant to, and Amendments to, the Merger Agreement.

(a) Pursuant to Section 1.01(c) of the Merger Agreement, the Company hereby consents to the extension by Purchaser of the Expiration Date to May 31, 2011.

(b) Clause (iii)(C) of Section 5.05(b) of the Merger Agreement is hereby amended and restated as follows:

(C) within 9 months after such termination, the Company enters into a definitive Contract to consummate, or consummates, the transactions contemplated by any Takeover Proposal (regardless of whether such Takeover Proposal is made before or after termination of this Agreement)

ARTICLE III

MISCELLANEOUS

Section 3.1 No Further Amendment. Except as expressly amended hereby, the Merger Agreement is in all respects ratified and confirmed and all the terms, conditions, and provisions thereof shall remain in full force and effect. This Amendment is limited precisely as written and shall not be deemed to be an amendment to any other term or condition of the Merger Agreement or any of the documents referred to therein.

Section 3.2 Effect of Amendment. This Amendment shall form a part of the Merger Agreement for all purposes, and each party thereto and hereto shall be bound hereby. From and after the execution of this Amendment by the parties hereto, any reference to the Merger Agreement shall be deemed a reference to the Merger Agreement as amended hereby.

Section 3.3 Governing Law. THIS AGREEMENT SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF DELAWARE, REGARDLESS OF THE LAWS THAT MIGHT OTHERWISE GOVERN UNDER APPLICABLE PRINCIPLES OF CONFLICTS OF LAWS THEREOF.

Section 3.4 Miscellaneous. Sections 8.02 [Notices], 8.04 [Interpretation], 8.05 [Consents and Approvals], 8.06 [Counterparts], 8.07 [Entire Agreement; No Third-Party Beneficiaries], 8.09 [Assignment], 8.10 [Specific Enforcement; Consent to Jurisdiction], 8.11 [Waiver of Jury Trial] and 8.12 [Severability] of the Merger Agreement shall apply to this Amendment mutatis mutandis.

[signature page follows]

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IN WITNESS WHEREOF, Parent, Merger Sub and the Company have caused this Agreement to be signed by their respective officers hereunto duly authorized, all as of the date first written above.

CHESAPEAKE ENERGY CORPORATION
By:	/s/ Domenic J. Dell’Osso, Jr.
Name:	Domenic J. Dell’Osso, Jr.
Title:	Executive Vice President and Chief Financial Officer

NOMAC ACQUISITION, INC.
By:	/s/ Domenic J. Dell’Osso, Jr.
Name:	Domenic J. Dell’Osso, Jr.
Title:	Executive Vice President and Chief Financial Officer

[SIGNATURE PAGE TO AMENDMENT NO. 1 TO AGREEMENT AND PLAN OF MERGER]

BRONCO DRILLING COMPANY, INC.
By:	/s/ D. Frank Harrison
Name:	D. Frank Harrison
Title:	Chairman and Chief Executive Officer

[SIGNATURE PAGE TO AMENDMENT NO. 1 TO AGREEMENT AND PLAN OF MERGER]