**Background of the Merger (beginning on page 35)**The following shall be added as the last sentence of the paragraph beginning, “Beginning in lateDecember 2010...” on page 37:**Mr. Jennings and the other board members believed that it was in the interests of Frontiershareholders to structure any potential transaction with Holly as a stock transaction and a truemerger of equals in light of the benefits of providing Frontier shareholders a continuing equityinterest in the combined company, the comparable levels of complexity and performance of the twocompanies over time, the objective of conserving cash and maintaining prudent debt levels for thecombined company, and the desire to combine the strengths of both companies.**The following shall be substituted for the first sentence of the paragraph beginning, “On December9, 2010, Mr. Clifton ...” on page 36:On December 9, 2010, Mr. Clifton met with Mr. Jennings in Dallas. At this meeting, Messrs. Cliftonand Jennings discussed their views regarding the potential strategic and financial benefits of amerger between Holly and Frontier, based solely on publicly available information. In addition,they discussed their views on the industry’s prospects,**including continuing volatilityin crack spreads and the industry trend toward greater scale and complexity of operations. Theyalso discussed** the economy as a whole and the potential benefits of a business combination interms of size and diversification.The following shall be substituted for the paragraph beginning, “On December 17, 2010, Messrs.Clifton and Jennings ...” on page 37:On December 17, 2010, Messrs. Clifton and Jennings had a follow-up meeting in Dallas to continuediscussions. Each outlined his views on what roles their respective executive management teamsmight have in the combined company and agreed on the need for management continuity in connectionwith integrating the two companies. **In general terms, they discussed ways to combine the skillsof each of the various executive officers of Holly and Frontier to benefit the combined companygoing forward, including what their own roles might be and the roles of other executive officers.They discussed the benefits of having a separate executive chairman and chief executive officer whowould combine leadership of Holly and Frontier and provide continuity of management for thecombined company.** Both agreed that a business combination between the two companies remained amutually desirable prospect as a merger of equals at market, such as a 30-day average closing priceof the common stock of the two companies. Mr. Jennings noted financing-related benefits that mightcome from a stronger combined balance sheet and ability to access more trade credit with suppliers.The following shall be substituted for the paragraph beginning, “On February 4, 2011, the Frontierboard of directors ...” on page 39:On February 4, 2011, the Frontier board of directors held a special meeting in Houston, togetherwith members of Frontier’s management and legal and financial advisors. Mr. Jennings provided anoverview of the potential transaction, to be structured as a merger of equals, and the progress ofthe transaction to date. Andrews Kurth advised the board regarding its fiduciary duties inconnection with considering a possible business combination, and the importance of board review anddeliberations. Andrews Kurth also presented an overview of the draft merger agreement as proposedby Holly, which had been previously distributed to the board. The board discussed the terms to benegotiated in the merger agreement, including the non-solicitation provisions and size of thebreak-up fee**, and while no specific terms or amounts were discussed, the board noted that thoseprovisions should be reciprocal and customary.** Frontier’s financial advisors discussed with theboard certain financial aspects relating to the potential merger.The following shall be added as the last sentence of the paragraph beginning, “On January 14,2011...” on page 38:
 

 
**The merger was viewed at all times by both Holly and Frontier as a merger of equals.Accordingly, during the course of negotiations, Holly and Frontier discussed that the exchangeratio would largely be based on the relative trading prices of the common stock of Holly andFrontier, including the current trading price, the five-day average closing price, and the 30-dayaverage closing price, all of which would necessarily be constantly changing as the partiesnegotiated the merger agreement.****Opinions of Holly’s Financial Advisors — Opinion of Morgan Stanley & Co. Incorporated (beginning onpage 45)**The following shall be substituted for the first sentence of the paragraph beginning, “MorganStanley calculated the exchange ratio . . .” on page 47:Morgan Stanley calculated the exchange ratio implied by the analyst price targets for Holly andFrontier (only with respect to **the nine** analysts that published price targets for bothHolly and Frontier) by dividing the Frontier price target by the Holly price target provided by thesame analyst.The following shall be added as the second sentence of the paragraph beginning, “Morgan Stanleycalculated the exchange ratio . . .” on page 47:**The Holly price targets published by these nine selected brokers ranged from $40 to $77 pershare, and the Frontier price targets published by these nine selected brokers ranged from $19 to$33 per share.**The following shall be substituted for the lead-in paragraph to the table on page 49:Based on the consensus estimates, the estimated value of Holly’s interests in HEP and the UNEVPipeline and each company’s respective forecasted outstanding net debt as of December 31, 2010,~~with~~**assuming $115 million of**Holly’~~s~~net debt **(** unconsolidated for HEP’~~s~~net debt **)**, Morgan Stanley estimated the following implied value ranges for shares ofFrontier and Holly, respectively, on a fully diluted basis:The following shall be substituted for the paragraph beginning, “In arriving at the estimatedequity values...” on page 50:In arriving at the estimated equity values per share of Frontier or Holly common stock, asapplicable, Morgan Stanley estimated a range of terminal values by multiplying Frontier’s orHolly’s estimated mid-cycle EBITDA (based on the 2006-2010 average prices of selected commodities,when full year data were available) by EBITDA multiples ranging from 4.5x to 6.0x. Morgan Stanleythen discounted Frontier’s or Holly’s forecasted unlevered free cash flows, as applicable, definedas net operating profit after tax plus depreciation and amortization, **stock-basedcompensation**, other non-cash items and net proceeds from asset sales less changes inworking capital, changes in other assets and liabilities and capital expenditures, and theestimated terminal value, in each case to a present value using discount rates ranging from 9.0% to11.0%. These discount rates were based on Morgan Stanley’s judgment of the estimated range ofFrontier’s or Holly’s weighted average cost of capital, as applicable.The following shall be substituted for the first sentence of the paragraph beginning, “Under theterms of its engagement letter, Morgan Stanley...” on page 52:Under the terms of its engagement letter, Morgan Stanley provided Holly with financial advisoryservices in connection with the merger for which it will be paid a fee of $5,125,000, ~~aportion~~**$1,500,000** of which became payable at the time of public announcement of the mergerand ~~a substantial portion~~**$3,625,000** of which is contingent upon, and will become payableupon, completion of the merger.**Opinions of Holly’s Financial Advisors — Opinion of Deutsche Bank Securities Inc. (beginning onpage 52)**The following shall be substituted for the paragraph beginning, “Deutsche Bank noted that the rangeof undiscounted...” on page 55:
 

 
Deutsche Bank noted that the range of undiscounted equity analyst price targets of Frontier commonstock was between $19.00 and $33.00 per share ~~and~~**based on a set of 11 equity research analystswho published recent price targets for Frontier common stock. Deutsche Bank also noted that**the range of undiscounted equity analyst price targets of Holly common stock was between $40.00 and$77.00 **per share based on a set of nine equity research analysts who published recent pricetargets for Holly common stock. Of the nine equity research analysts who published recent pricetargets for both Frontier and Holly, the range of undiscounted price targets of Frontier commonstock was between $19.00 and $33.00** per share. Deutsche Bank calculated that the impliedexchange ratio based on the price targets of the nine equity research analysts who published pricetargets for both Frontier and Holly ranged from 0.4151x to 0.5167x as compared to the exchangeratio of 0.4811x.The following shall be substituted for the first two sentences of the paragraph titled,“—Discounted Cash Flow Analysis” on page 56:*Discounted Cash Flow Analysis*. Deutsche Bank performed a discounted cash flow analysis todetermine a range of implied present values per share of Frontier common stock based on projectedunlevered free cash flows for Frontier on a standalone basis for the years ending December 31, 2011through 2015, using estimates from Holly management. ~~The~~**For the purposes of this calculation,unlevered free cash flow was calculated as (1) tax adjusted earnings before interest and taxes plus(2) depreciation and amortization less (3) capital expenditures less (4) increases in workingcapital plus (5) stock-based compensation expenses, changes in other assets and changes in otherliabilities. Stock-based compensation was not treated as a cash expense in Deutsche Bank’sanalysis. Deutsche Bank’s** analysis was based on a range of discount rates from 9.0%to 11.0% and a terminal value based on multiples ranging from 5.0x to 6.0x applied to Frontier’smid-cycle EBITDA.The following shall be substituted for the second sentence of the paragraph beginning, “The Hollyboard of directors engaged Deutsche Bank...” on page 58:Pursuant to its engagement letter with Holly, Deutsche Bank will be paid a transaction fee of$4,875,000 for its services as financial advisor to Holly in connection with the merger, ~~a portion~~of which **$1,500,000** was paid upon delivery of its opinion and ~~a substantial portion~~ ofwhich **$3,375,000** is payable contingent upon completion of the merger.**Opinions of Frontier’s Financial Advisors — Opinion of Credit Suisse Securities (USA) LLC(beginning on page 63)**The following shall be added immediately after the first paragraph under, “—Discounted Cash FlowAnalysis” on page 68:**For purposes of the discounted cash flow analyses, the free cash flows for Holly’s refiningbusiness and for Frontier were calculated based on the projected EBITDA for Holly’s refiningbusiness and for Frontier, as appropriate, less cash taxes, capital expenditures and turnaroundexpenses plus changes in net working capital and the proceeds from asset sales, in each case asprovided by Frontier management; the free cash flows for Holly’s limited partnership interests inHEP were calculated based on the projected operating cash flow available for distribution to HEP’slimited partners, as provided by Frontier’s management; and the free cash flows for Holly’s generalpartnership interests in HEP were calculated based on Holly’s general partnership interest andincentive distribution rights in the projected after-tax operating cash flows available fordistribution to HEP’s partners, as provided by Frontier’s management.**The following shall be substituted for the first paragraph under, “—Discounted Cash FlowsAnalysis” on page 68:Credit Suisse also calculated implied exchange ratio reference ranges based on the net presentvalue of Holly’s free cash flows through 2015 and the net present value of Frontier’s free cashflows through 2015. For purposes of this analysis, Credit Suisse used the financial forecasts forHolly developed based on assumptions provided by and discussions with the management of Frontierfrom estimates of prospective financial and operating data provided to Credit Suisse by themanagement of Holly and the financial forecasts for Frontier provided by the management ofFrontier. In performing this analysis, Credit Suisse applied discount rates ranging from 9.0% to11.5% ~~and terminal~~
 

 
~~EBITDA multiples of 6.50x to 7.50x~~ to the projected unlevered free cash flows from Holly~~’s refining business~~**’s refining business taking into consideration, among other things, Holly’sweighted average cost of capital and a terminal value calculated using EBITDA multiples of 6.50x to7.50x taking into consideration, among other things, the selected companies analyses with respectto Holly**; discount rates ranging from 7.5% to 9.5%~~and~~**to the projected levered free cashflows from Holly’s limited partnership interests in HEP taking into consideration, among otherthings, Holly’s cost of equity and a** terminal **value calculated using** LP distributedcash flow yields of 6.75% to 7.25% ~~to the projected levered free cash flows from Holly’~~**takinginto consideration, among other things, the selected companies analyses with respect toHolly**’s limited partnership interests in HEP; and discount rates ranging from 12.0% to14.0% ~~and~~**to the projected levered free cash flows from Holly’s general partnership interests inHEP taking into consideration, among other things, Holly’s cost of equity and a** terminal **value calculated using** GP distributed cash flow yields of 4.75% to 6.00% ~~to the projectedlevered free cash flows from Holly’~~**taking into consideration, among other things, the selectedcompanies analyses with respect to Holly**’s general partnership interests in HEP,~~respectively.~~ With respect to Frontier, in performing this analysis, Credit Suisse applied discountrates ranging from 9.0% to 11.5% ~~and~~**to Frontier’s projected unlevered free cash flows takinginto consideration, among other things, Frontier’s weighted average cost of capital and aterminal value calculated using** EBITDA multiples of 6.50x to 7.50x **taking intoconsideration, among other things, the selected companies analyseswith respect** to Frontier’s~~projected unlevered free cash flows~~. This analysis indicated an implied exchange ratio referencerange of 0.348 to 0.499 of a share of Holly common stock per share of Frontier common stock, ascompared to the exchange ratio in the proposed merger of 0.4811 of a share of Holly common stockper share of Frontier common stock.The following table shall be inserted immediately following the first paragraph under“—Contribution Analysis” on page 69:     Metric Implied Exchange Ratio Adjusted EBITDA    2010 E  0.352x 2011E  0.501x 2012E  0.473x Adjusted Refining EBITDA    2010E  0.335x 2011E  0.449x 2012E  0.435x Net Income    2010E  0.182x 2011E  0.419x 2012E  0.481x The following shall be substituted for the second sentence under “—Other Matters” on page 69:Credit Suisse will receive an aggregate fee of $5 million for its services, ~~a substantial portion~~of which **$3.5 million** is contingent upon completion of the merger.**Opinions of Frontier’s Financial Advisors — Opinion of Citigroup Global Markets Inc. (beginning onpage 70)**The following shall be substituted for the second and third sentences of the paragraph“—Discounted Cash Flow Analysis — Frontier” on page 74:**Based on such internal estimates of Frontier’s****management, the free cash flows werecalculated as adjusted EBITDA less cash taxes, turnaround expenditures, capital expenditures andchanges in net working capital.** Estimated terminal values for Frontier were calculated byapplying **to Frontier’s fiscal year 2015 estimated EBITDA** a range of terminal value EBITDAmultiples of 6.5x to 7.75x ~~to Frontier’s fiscal year2015 estimated EBITDA.~~**, which range wasselected taking into consideration, among other things, estimated EBITDA trading multiples of theselected refining companies referred to above under the caption “Selected Public CompaniesAnalysis.”** The cash flows and terminal values were then discounted to present value usingdiscount rates
 

 
ranging from 9.31% to 10.92%, **which range was selected taking into consideration, among otherthings, a weighted average cost of capital calculation**.The following shall be substituted for the second and third sentences of the paragraph“—Discounted Cash Flow Analysis — Holly — Refinery Assets” on page 74:**Based on such internal financial information relating to Holly’s fiscal year-ended December 31,2010 provided by Holly’s management and financial forecasts relating to Holly derived from certaininternal operating data and estimates provided by Holly’s management and other assumptions preparedby Frontier’s management, the free cash flows were calculated as adjusted EBITDA plus estimatedproceeds from Holly’s sale of its interest in UNEV Pipeline, L.L.C. to HEP in 2012, less cashtaxes, turnaround expenditures, capital expenditures and changes in net working capital.**Estimated terminal values for Holly’s refinery assets were calculated by applying **to the fiscalyear 2015 estimated EBITDA of Holly’s refinery assets** a range of terminal value EBITDAmultiples of 6.5x to 7.75x ~~to the fiscal year 2015 estimated EBITDA of Holly’s refineryassets.,~~**which range was selected taking into consideration, among other things, estimatedEBITDA trading multiples of the selected refining companies referred to above under the caption“Selected Public Companies Analysis.”**The cash flows and terminal values were then discountedto present value using discount rates ranging from 9.31% to 10.92%**, which range was selectedtaking into consideration, among other things, a weighted average cost of capital calculation**.The following shall be substituted for the second and third sentences of the paragraph“—Discounted Cash Flow Analysis — Holly — GP Interest” on page 75:**Based on such internal financial information relating to Holly’s fiscal year-endedDecember 31, 2010 provided by Holly’s management and financial forecasts relating to Holly derivedfrom certain internal operating data and estimates provided by Holly’s management and otherassumptions prepared by Frontier’s management, the distribution in respect of Holly’s GP interestwas calculated based on Holly’s GP interest and incentive distribution rights in HEP’s projectedoperating cash flows distributed to HEP’s partners less taxes.** Estimated terminal values forHolly’s GP interest were calculated by applying ~~a range of terminal value distributionyields of 5.0% to 6.0%~~ to the fiscal year 2015 estimated after-tax distributions in respect of suchGP interests **a range of terminal value distribution yields of 5.0% to 6.0%, which range wasselected taking into consideration, among other things, estimated distribution yields of theselected GPs referred to above under the caption “SelectedPublic Companies Analysis.”** Thedistributions and terminal values were then discounted to present value using discount ratesranging from 9.26% to 11.64%**, which range was selected taking into consideration, among otherthings, a cost of equity calculation**.The following shall be substituted for the second and third sentences of the paragraph“—Discounted Cash Flow Analysis — Holly — LP Interest” on page 75:**Based on such internal financial information relating to Holly’s fiscal year-endedDecember 31, 2010 provided by Holly’s management and financial forecasts relating to Holly derivedfrom certain internal operating data and estimates provided by Holly’s management and otherassumptions prepared by Frontier’s management, the distributable cash flow per unit****wascalculated based on HEP’s projected operating cash flow available for distribution to HEP’s limitedpartners.** Estimated terminal values for HEP were calculated by applying **to HEP’s fiscalyear 2015 estimated distributable cash flow per unit** a range of terminal value distributablecash flow yields of 6.25% to 7.0% ~~to HEP’s fiscal year2015,~~**which range was selected takinginto consideration, among other things, implied yields based on** estimated distributable cashflow ~~per unit.~~**trading multiples of the selected MLPs referred to above under the caption“Selected Public Companies Analysis.**”**The distributable cash flow and terminal values werethen discounted to present value using discount rates ranging from 7.76% to 9.14% **, which rangewas selected taking into consideration, among other things, a cost of equity calculation**.
 

 
The following shall be substituted for the first sentence under “—Miscellaneous” on page 75:Under the terms of Citi’s engagement, Frontier has agreed to pay Citi for its financial advisoryservices in connection with the merger an aggregate fee of $5 million, a portion of which waspayable upon delivery of Citi’s opinion and ~~a significant portion~~**$3.5 million**of which iscontingent upon completion of the merger.**Important Information for Investors and Shareholders**This communication does not constitute an offer to sell or the solicitation of an offer to buy anysecurities or a solicitation of any vote or approval. The issuance of Holly common stock inconnection with the proposed merger has been submitted to Holly’s stockholders for theirconsideration, and the proposed merger has been submitted to shareholders of Frontier Oil for theirconsideration. Holly has filed with the Securities and Exchange Commission (“SEC”) a registrationstatement on Form S-4 that includes a joint proxy statement to be used by Holly and Frontier tosolicit the required approval of their shareholders in connection with the proposed merger andconstituted a prospectus of Holly, which the SEC has declared effective. Holly and Frontier mayalso file other documents with the SEC concerning the proposed merger. **INVESTORS AND SECURITYHOLDERS OF HOLLY AND FRONTIER ARE URGED TO READ THE JOINT PROXY STATEMENT/PROSPECTUS REGARDING THEPROPOSED MERGER AND OTHER RELEVANT DOCUMENTS FILED WITH THE SEC CAREFULLY AND IN THEIR ENTIRETYBECAUSE THEY CONTAIN IMPORTANT INFORMATION ABOUT THE PROPOSED MERGER.**Investors and securityholders may obtain a free copy of the joint proxy statement/prospectus and other documentscontaining important information about Holly and Frontier through the website maintained by the SECat www.sec.gov. Copies of the documents filed with the SEC by Holly are available free ofcharge on Holly’s website at www.hollycorp.com under the tab “Investors” or by contactingHolly’s Investor Relations Department at (214) 871-3555. Copies of documents filed with the SEC byFrontier are available free of charge on Frontier’s website at www.frontieroil.com underthe tab “Investor Relations” and then under the tab “SEC Filings” or by contacting Frontier’sInvestor Relations Department at (713) 688-9600.Holly, Frontier and certain of their respective directors and executive officers may be deemed tobe participants in the solicitation of proxies from the stockholders of Holly and shareholders ofFrontier in connection with the proposed transaction. Information about the directors and executiveofficers of Holly is set forth in its proxy statement for its 2011 annual meeting of stockholders,which was filed with the SEC on March 31, 2011. Information about the directors and executiveofficers of Frontier is set forth in its proxy statement for its 2011 annual meeting ofshareholders, which was filed with the SEC on March 21, 2011. These documents can be obtained freeof charge from the sources indicated above. Other information regarding the participants in theproxy solicitation and a description of their direct and indirect interests, by security holdingsor otherwise, are contained in the joint proxy statement/prospectus and other relevant materialsfiled with the SEC.**Cautionary Statement Regarding Forward-Looking Statements**This communication contains “forward-looking” statements within the meaning of Section 27A of theSecurities Act of 1933, and Section 21E of the Securities Exchange Act of 1934. These includestatements regarding the effects of the proposed merger and statements preceded by, followed by orthat otherwise include the words “believes,” “expects,” “anticipates,” “intends,” “estimates,” orsimilar expressions. Forward looking statements relating to expectations about future results orevents are based upon information available to Holly and Frontier as of today’s date, and are notguarantees of the future performance of Holly, Frontier or the combined company, and actual resultsmay vary materially from the results and expectations discussed. For instance, there is noassurance that the proposed merger will be consummated. The merger agreement will terminate if thecompanies do not receive the necessary approval of Holly’s stockholders or Frontier’s shareholdersor government approvals or if either Holly or Frontier fails to satisfy conditions to closing.Additional risks and uncertainties related to the proposed merger include, but are not limited to,the successful integration of Holly’s and Frontier’s businesses and the combined company’s abilityto compete in the highly competitive refining and marketing industry. The revenues, earnings andbusiness prospects of Holly, Frontier and the combined company and their ability to achieve plannedbusiness objectives will be subject to a number of risks and uncertainties. These risks anduncertainties include, among other things, risks and uncertainties with respect to the actions ofactual or potential competitive suppliers of refined petroleum products in Holly’s, Frontier’s andthe combined company’s markets; the demand for and supply of crude oil and refined products; thespread between market prices for refined products and market prices for crude oil; the
 

 
possibility of constraints on the transportation of refined products; the possibility ofinefficiencies, curtailments or shutdowns in refinery operations or pipelines; effects ofgovernmental and environmental regulations and policies; the availability and cost of financing;the effectiveness of capital investments and marketing strategies; efficiency in carrying outconstruction projects; the ability to acquire refined product operations or pipeline and terminaloperations on acceptable terms and to integrate any existing or future acquired operations; thepossibility of terrorist attacks and the consequences of any such attacks; and general economicconditions.**Holly and Frontier caution that the foregoing list of risks and uncertainties is not exclusive.Additional information concerning these and other risks is contained in Holly’s and Frontier’s mostrecently filed Annual Report on Form 10-K, subsequent Quarterly Report on Form 10-Q, recent CurrentReports on Form 8-K and other SEC filings. All subsequent written and oral forward-lookingstatements concerning Holly, Frontier, the proposed merger or other matters and attributable toHolly or Frontier or any person acting on their behalf are expressly qualified in their entirety bythe cautionary statements above. Neither Holly nor Frontier undertake any obligation to publiclyupdate any of these forward-looking statements to reflect events or circumstances that may ariseafter the date hereof.**
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