Basic net loss attributable to Vertex per common share is based upon the weighted-average number of common shares outstanding during the period, excluding restricted stock and restricted stock units that have been issued but are not yet vested. Diluted net loss attributable to Vertex per common share is based upon the weighted-average number of common shares outstanding during the period plus additional weighted-average common equivalent shares outstanding during the period when the effect is dilutive. Common equivalent shares result from the assumed exercise of outstanding stock options (the proceeds of which are then assumed to have been used to repurchase outstanding stock using the treasury stock method), the assumed conversion of convertible notes and vesting of unvested restricted stock and restricted stock units. Common equivalent shares have not been included in the net loss attributable to Vertex per common share calculations because the effect would have been anti-dilutive. Total potential gross common equivalent shares consisted of the following:

		At June 30,

		2011		2010
		(in thousands, except per share amounts)
Stock options			20,589		20,993
	Weighted-average exercise price (per share)	$	32.43	$	32.07
Convertible senior subordinated notes			8,192		—
	Conversion price (per share)	$	48.83		n/a
Unvested restricted stock and restricted stock units			1,971		1,871

The Company reviews each collaboration agreement pursuant to which the Company licenses assets owned by a collaborator in order to determine whether or not the collaborator is a VIE. If the collaborator is a VIE, the Company assesses whether or not the Company is the primary beneficiary of that VIE based on a number of factors, including (i) which party has the power to direct the activities that most significantly affect the VIE's economic performance, (ii) the parties' contractual rights and responsibilities pursuant to the collaboration and (iii) which party has the obligation to absorb losses or the right to receive benefits from the VIE. If the Company is determined to be the primary beneficiary of a VIE, the Company consolidates the statements of operations and financial condition of the VIE into the Company's condensed consolidated financial statements. As of June 13, 2011 (the effective date of the Company's collaboration with Alios) and June 30, 2011, the Company evaluated its collaboration with Alios (the "Alios Collaboration") and determined that Alios is a VIE and that the Company is Alios' primary beneficiary. The Company will re-evaluate its collaboration with Alios each reporting period in order to determine if there are changes in circumstances that would result in the Company ceasing to consolidate the statements of operations and financial condition of Alios into the Company's condensed consolidated financial statements. The Company would deconsolidate Alios if Alios ceased to be a VIE or if the Company was no longer Alios' primary beneficiary. Please refer to Note K, "Collaborative Arrangements," for further information.

The Company expenses the fair value of employee stock options and other forms of stock-based employee compensation over the associated employee service period or, for awards with market conditions, the derived service period. For awards with performance conditions, the Company makes estimates regarding the likelihood of satisfaction of the performance conditions that affect the period over which the expense is recognized. Compensation expense is determined based on the fair value of the award at the grant date, including estimated forfeitures, and is adjusted each period to reflect actual forfeitures and the outcomes of certain market and performance conditions. Please refer to Note C, "Stock-based Compensation Expense," for further information.

The Company expenses as incurred all research and development expenses, including amounts funded by research and development collaborations. The Company defers and capitalizes nonrefundable advance payments made by the Company for research and development activities until the related goods are delivered or the related services are performed.

Research and development expenses are comprised of costs incurred by the Company in performing research and development activities and include: salary and benefits; stock-based compensation expense; laboratory supplies and other direct expenses; contractual services costs, including clinical trial and pharmaceutical development costs; expenses associated with commercial supplies that are not being capitalized; and infrastructure costs, including facilities costs and depreciation expense. The Company evaluates periodically what portion of its commercial supply costs may be capitalized as described below in the Company's accounting policy regarding inventories.

The Company's collaborators funded portions of the Company's research and development programs related to specific drug candidates and research targets, including telaprevir, VX-661 and research directed toward identifying additional corrector compounds for the treatment of cystic fibrosis in the three and six months ended June 30, 2011, and telaprevir in the three and six months ended June 30, 2010. The Company's collaborative revenues, including amortization of up-front license fees received in prior periods, were $29.9 million and $24.4 million, respectively, for the three months ended June 30, 2011 and 2010, and $97.5 million and $40.4 million, respectively, for the six months ended June 30, 2011 and 2010. The Company's research and development expenses allocated to programs in which a collaborator funded at least a portion of the research and development expenses were approximately $40 million in both the three months ended June 30, 2011 and the three months ended June 30, 2010, and approximately $64 million and $77 million, respectively, for the six months ended June 30, 2011 and 2010.

The Company values its inventories at the lower of cost or market. The Company determines the cost of its inventories, which includes amounts related to materials and manufacturing overhead, on a first-in, first-out ("FIFO") basis. If the Company identifies excess, obsolete or unsalable items, its inventories are written down to their realizable value in the period that the impairment is first identified.

The Company capitalizes inventories produced in preparation for initiating sales of a drug candidate when the related drug candidate is considered to have a high likelihood of regulatory approval and the related costs are expected to be recoverable through sales of the drug. In determining whether or not to capitalize such inventory, the Company evaluates, among other factors, information regarding the drug candidate's safety and efficacy, the status of regulatory submissions and communications with regulatory authorities and the outlook for commercial sales, including the existence of current or anticipated competitive drugs and the availability of reimbursement. In addition, the Company evaluates risks associated with manufacturing the drug candidate and the remaining shelf life of the inventory. Please refer to Note H, "Inventories," for further information.

The Company records costs and liabilities associated with exit and disposal activities based on estimates of fair value in the period the liabilities are incurred. In periods subsequent to the Company's initial measurement, the Company measures changes to the liability using the credit-adjusted risk-free discount rate it applied in the initial period. The Company evaluates and adjusts these liabilities as appropriate for changes in circumstances at least on a quarterly basis. Please refer to Note I, "Restructuring Expense," for further information.

The Company sells INCIVEK principally to a limited number of major wholesalers, as well as selected regional wholesalers and specialty pharmacy providers (collectively, its "Distributors") that subsequently resell INCIVEK to patients and healthcare providers. The Company recognizes net product revenues from sales of INCIVEK upon delivery to the Distributor as long as (i) there is persuasive evidence that an arrangement exists between the Company and the Distributor, (ii) collectibility is reasonably assured and (iii) the price is fixed or determinable.

The Company has written contracts with its Distributors and delivery occurs when a Distributor receives INCIVEK (freight on board destination). The Company evaluates the creditworthiness of each of its Distributors to determine whether revenues can be recognized upon delivery, subject to satisfaction of the other requirements, or whether recognition is required to be delayed until receipt of payment. In order to conclude that the price is fixed or determinable, the Company must be able to (i) calculate its gross product revenues from the sales to Distributors and (ii) reasonably estimate its net product revenues. The Company calculates gross product revenues based on the wholesale acquisition cost that the Company charges its Distributors for INCIVEK. The Company estimates its net product revenues by deducting from its gross product revenues (i) trade allowances, such as invoice discounts for prompt payment and distributor fees, (ii) estimated government and private payor rebates, chargebacks and discounts, such as Medicaid reimbursements, (iii) reserves for expected product returns and (iv) estimated costs of incentives offered to certain indirect customers including patients.

The following table summarizes activity in each of the above product revenue allowances and reserve categories for the three-month period from March 31, 2011 to June 30, 2011:

		Trade Allowances			Rebates, Chargebacks and Discounts		Product Returns		Other Incentives		Total

		(in thousands)
Balance at March 31, 2011		$	—		$	—	$	—	$	—	$	—
	Provision related to second quarter of 2011 sales		2,782			3,744		76		1,416		8,018
	Payments (credits)		(19	)		—		—		—		(19	)

Balance at June 30, 2011		$	2,763		$	3,744	$	76	$	1,416	$	7,999

Prior to the second quarter of 2011, the Company's revenues were generated primarily through collaborative research, development and/or commercialization agreements. The terms of these agreements typically include payment to the Company of one or more of the following: nonrefundable, up-front license fees; milestone payments; funding of research and/or development activities; payments for services the Company provides through its third-party manufacturing network; and royalties on product sales. Each of these types of payments results in collaborative revenues, except for revenues from royalties on product sales, which are classified as royalty revenues.

Collaborative research, development and/or commercialization agreements entered into prior to January 1, 2011 that contain multiple elements of revenue are divided into separate units of accounting if certain criteria are met, including whether the delivered element has stand-alone value to the collaborator and whether there is objective and reliable evidence of the fair value of the undelivered obligation(s). The Company allocates consideration it receives among the separate units either on the basis of each unit's fair value or using the residual method, and applies the applicable revenue recognition criteria to each of the separate units.

The Company recognizes revenues from nonrefundable, up-front license fees on a straight-line basis over the contracted or estimated period of performance, which is typically the period over which the research and development is expected to occur or manufacturing services are expected to be provided. In order to estimate the period of performance, the Company is required to make estimates regarding the drug development and commercialization timelines for drug candidates being developed pursuant to the applicable agreement. The Company's estimates regarding the period of performance under certain of its collaboration agreements have changed in the past and may change in the future.

At the inception of each agreement that includes milestone payments, the Company evaluates whether each milestone is substantive on the basis of the contingent nature of the milestone, specifically reviewing factors such as the scientific and other risks that must be overcome to achieve the milestone, as well as the level of effort and investment required. The Company recognizes revenues related to substantive milestones in full in the period in which the substantive milestone is achieved, if payment is reasonably assured and the Company's performance obligations are fully satisfied or if the Company has fair value for its remaining obligations. If the Company has remaining obligations after the achievement of a substantive milestone and does not have sufficient evidence of the fair value of those obligations, the milestone payment is recognized over the period of performance. If a milestone is not considered substantive, the Company recognizes the applicable milestone payment over the remaining period of performance.

Under certain of its collaboration agreements, the Company is entitled to reimbursement from its collaborators for specified research and development expenses and/or payments for specified manufacturing services that the Company provides through its third-party manufacturing network. The Company considers the nature and contractual terms of the arrangement and the nature of the Company's business operations in order to determine whether research and development funding will result in collaborative revenues or an offset to research and development expenses. The Company typically recognizes the revenues related to these reimbursable expenses and manufacturing services in the period in which the reimbursable expenses are incurred or the manufacturing services are provided.

On January 1, 2011, updated guidance on the recognition of revenues for agreements with multiple deliverables became effective and applies to any agreements entered into by the Company on or after January 1, 2011. This updated guidance (1) relates to whether multiple deliverables exist, how the deliverables in a revenue arrangement should be separated and how the consideration should be allocated; (2) requires companies to allocate revenues in an arrangement using estimated selling prices of deliverables if a vendor does not have vendor-specific objective evidence or third-party evidence of selling price; and (3) eliminates the use of the residual method and requires companies to allocate revenues using the relative selling price method. During the first half of 2011, the Company did not enter into any agreements that would be accounted for by the Company pursuant to this updated guidance. If the Company enters into an agreement with multiple deliverables after January 1, 2011, this updated guidance could have a material effect on the Company's financial statements.

The Company typically recognizes royalty revenues based upon actual and estimated net sales of licensed products in licensed territories, as provided by the licensee, and generally recognizes royalty revenues in the period the sales occur. The Company reconciles and adjusts for differences between actual royalty revenues and estimated royalty revenues in the quarter they become known. These differences historically have not been significant.

The Company has sold its rights to receive certain royalties on sales of HIV protease inhibitors and recognizes the revenues related to this sale as royalty revenues. In the circumstance where the Company has sold its rights to future royalties under a license agreement and also maintains continuing involvement in the royalty arrangement (but not significant continuing involvement in the generation of the cash flows payable to the purchaser of the future royalty rights), the Company defers recognition of the proceeds it receives for the royalty stream and recognizes these deferred revenues over the life of the license agreement pursuant to the units-of-revenue method. Under this method, the amount of deferred revenues to be recognized as royalty revenues in each period is calculated by multiplying the following: (1) the royalty payments payable to the purchaser for the period by (2) the ratio of the remaining deferred revenue amount to the total estimated remaining royalty payments payable to the purchaser over the term of the agreement. The Company's estimates regarding the estimated remaining royalty payments due to the purchaser have changed in the past and may change in the future.

The Company assigns the value of consideration, including contingent consideration, transferred in business combinations based on their fair values as of the effective date of the transaction. The Company accounts for the Alios Collaboration as a business combination due to the determinations that (i) Alios is a VIE, (ii) Alios is a business and (iii) the Company is Alios' primary beneficiary. Transaction costs and any restructuring costs associated with these transactions are expensed as incurred.

Fair Value of In-process Research and Development Assets and Contingent Payments in Business Combinations

The Company assesses the fair value of assets, including the fair value of in-process research and development assets, and contingent payments pursuant to collaborations accounted for as business combinations, from the perspective of a market participant, using a variety of methods. The present-value models used to estimate the fair values of research and development assets and contingent payments pursuant to collaborations incorporate significant assumptions, including: assumptions regarding the probability of obtaining marketing approval and/or achieving relevant development milestones for a drug candidate; estimates regarding the timing of and the expected costs to develop a drug candidate; estimates of future cash flows from potential product sales and/or the potential to achieve certain commercial milestones with respect to a drug candidate; and the appropriate discount rates.

In-process research and development assets relate to (i) the Company's acquisition of ViroChem in March 2009 and (ii) the Alios Collaboration, which the Company entered into in June 2011. The Company records the value of in-process research and development assets at their fair value as of the transaction date. These assets are accounted for as indefinite-lived intangible assets and maintained on the Company's condensed consolidated balance sheets until either the project underlying them is completed or the assets become impaired. If a project is completed, the carrying value of the related intangible asset is amortized as a part of cost of product revenues over the remaining estimated life of the asset beginning in the period in which the project is completed. If a project becomes impaired or is abandoned, the carrying value of the related intangible asset is written down to its fair value and an impairment charge is taken in the period in which the impairment occurs. In-process research and development assets are tested for impairment on an annual basis as of October 1, and more frequently if indicators are present or changes in circumstances suggest that impairment may exist.

The difference between the purchase price and the fair value of assets acquired and liabilities assumed in a business combination, or deemed to be acquired or assumed in other business transactions treated as business combinations for accounting purposes, is allocated to goodwill. As of December 31, 2010, goodwill related to the Company's acquisition of ViroChem. As of June 30, 2011, goodwill consists of goodwill related to the Company's acquisition of ViroChem and the Company's collaboration with Alios. Goodwill is evaluated for impairment on an annual basis as of October 1, and more frequently if indicators are present or changes in circumstances suggest that impairment may exist.

The Company has entered into financial transactions involving free-standing derivative instruments and embedded derivatives. These financial transactions include arrangements involving secured notes, the sale of potential future milestone payments and senior subordinated convertible notes. The embedded derivatives are required to be bifurcated from the host instruments because the derivatives are not clearly and closely related to the host instruments. The Company determines the fair value of each derivative instrument or embedded derivative on the date of issuance and at the end of each quarterly period. The estimates of the fair value of these derivatives, particularly with respect to derivatives related to the achievement of milestones in the development of telaprevir, include significant assumptions regarding the estimates market participants would make in order to evaluate these derivatives. Changes in the fair value of these derivatives are evaluated on a quarterly basis. Please refer to Note M, "September 2009 Financial Transactions," for further information.

In June 2011, the Financial Accounting Standards Board ("FASB") issued amended guidance intended to increase the prominence of items reported in other comprehensive income. The guidance requires that all nonowner changes in shareholders' equity be presented either in a single continuous statement of comprehensive income or in two separate but consecutive statements. The guidance will be applied retrospectively beginning on January 1, 2012, for interim and annual reporting. These amendments will not have a material effect on the Company's condensed consolidated financial statements.

In May 2011, the FASB amended guidance regarding the measurement of the fair value of assets and liabilities to harmonize the fair value measurement guidance under GAAP and under the International Financial Reporting Standards (IFRSs). This amended guidance clarifies the FASB's intent about the application of existing fair value measurement requirements and changes a particular principle or requirement for measuring fair value or for disclosing information about fair value measurements. The amendments will be applied prospectively and will become applicable to the Company's financial statements beginning on January 1, 2012. The Company currently is evaluating the effect that these amendments will have on the Company's condensed consolidated financial statements.

For a discussion of recent accounting pronouncements in addition to those discussed above, please refer to Note B "Accounting Policies—Recent Accounting Pronouncements" in the Company's Annual Report on Form 10-K. The Company did not adopt any new accounting pronouncements during the six months ended June 30, 2011 that had a material impact on the Company's condensed consolidated financial statements.