485BPOS

As filed with the Securities and Exchange Commission on December 28, 2012

Registration Nos. 333-89822; 811-21114

U.S. SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form N-1A

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933 x

Pre-Effective Amendment No.

Post-Effective Amendment No. 78

and/or

REGISTRATION STATEMENT

UNDER

THE INVESTMENT COMPANY ACT OF 1940 x

Amendment No. 87

ProShares Trust

(Exact name of Registrant as Specified in Trust Instrument)

7501 Wisconsin Avenue,

Suite 1000 Bethesda, MD 20814

(Address of Principal Executive Office) (Zip Code)

(240) 497-6400

(Area Code and Telephone Number)

Michael L. Sapir, CEO

ProShare Advisors LLC

7501 Wisconsin Avenue, Suite 1000

Bethesda, MD 20814

(Name and Address of Agent for Service)

with copies to:
John Loder, Esq. c/o Ropes & Gray LLP One International Place Boston, MA 02110	Amy R. Doberman ProShare Advisors LLC 7501 Wisconsin Avenue, Suite 1000 Bethesda, MD 20814

Approximate date of Proposed Public Offering:

It is proposed that this filing will become effective:

x immediately upon filing pursuant to paragraph (b)

¨ 60 days after filing pursuant to paragraph (a)(1)

¨ on      pursuant to paragraph (a)(1)

¨ 75 days after filing pursuant to paragraph (a)(2)

¨ on (date) pursuant to paragraph (a)(2) of rule 485.

If appropriate, check the following:

¨ This post-effective amendment designates a new effective date for a previously filed post-effective amendment.

EXPLANATORY NOTE

This post-effective amendment relates only to ProShares Merger ETF. No information relating to any other series or class of series of ProShares Trust is amended or superseded hereby.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933 and the Investment Company Act of 1940, the Registrant has duly caused this Post-Effective Amendment No. 78 to its Registration Statement to be signed on its behalf by the undersigned, thereto duly authorized, in the City of Bethesda and the State of Maryland on December 28, 2012.

ProShares Trust
By:	/s/ Louis M. Mayberg
	Louis M. Mayberg

Pursuant to the requirements of the Securities Act of 1933, this Amendment to the Registration Statement has been signed below by the following persons in the capacities indicated.

Signature	Title	Date
/s/ Michael L. Sapir * Michael L. Sapir	Trustee, Chairman	December 28, 2012
/s/ Russell S. Reynolds, III * Russell S. Reynolds, III	Trustee	December 28, 2012
/s/ Michael C. Wachs * Michael C. Wachs	Trustee	December 28, 2012
/s/ William D. Fertig* William D. Fertig	Trustee	December 28, 2012
/s/ Louis M. Mayberg * Louis M. Mayberg	President	December 28, 2012
/s/ Charles S. Todd Charles S. Todd	Treasurer	December 28, 2012

* By:	/s/ Amy R. Doberman
	Amy R. Doberman
	As Attorney-in-fact
Date:	December 28, 2012

Exhibit Index

EXHIBIT NUMBER	DESCRIPTION
EX-101.INS	XBRL Instance Document
EX-101.SCH	XBRL Taxonomy Extension Schema Document
EX-101.CAL	XBRL Taxonomy Extension Calculation Linkbase
EX-101.DEF	XBRL Taxonomy Extension Definition Linkbase
EX-101.LAB	XBRL Taxonomy Extension Label Linkbase
EX-101.PRE	XBRL Taxonomy Extension Presentation Linkbase

XML

ProShares Merger ETF

ProShares Merger ETF

Investment Objective

ProShares Merger ETF (the “Fund”) seeks investment results, before fees and expenses, that track the performance of the S&P Merger Arbitrage Index (the “Index”).

Fees and Expenses of the Fund

The table below describes the fees and expenses that you may pay if you buy or hold shares of the Fund.

Annual Fund Operating Expenses
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses		ProShares Merger ETF
Investment Advisory Fees		0.75%
Other Expenses	[1]	1.36%
Total Annual Fund Operating Expenses Before Fee Waivers and Expense Reimbursements		2.11%
Fee Waiver/Reimbursement	[2]	(1.36%)
Total Annual Fund Operating Expenses After Fee Waivers and Expense Reimbursements		0.75%

Example:

This example is intended to help you compare the cost of investing in the Fund with the cost of investing in other funds.

The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of each period. The example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same, except that the fee waiver/expense reimbursement is assumed only to pertain to the first year. Although your actual cost may be higher or lower, based on these assumptions your approximate costs would be:

Expense Example (USD $)	1 Year	3 Years
ProShares Merger ETF	77	530

The Fund pays transaction and financing costs associated with transacting in securities and derivatives. In addition, investors may pay brokerage commissions on their purchases and sales of the Fund’s shares. These costs are not reflected in the example or the table above.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the example above, affect the Fund’s performance. The Fund’s portfolio turnover rate is calculated without regard to cash instrument or derivatives transactions. If such transactions were included, the Fund’s portfolio turnover rate would be significantly higher. Although the Fund has not yet commenced operations as of the date of this Prospectus and no portfolio turnover information is provided for this Fund, the Fund expects its portfolio turnover rate to exceed 100%.

Principal Investment Strategies

The Fund is designed to track the performance of the Index and provide exposure to a global merger arbitrage strategy, which seeks to capture the spread between the price at which the stock of a company (each such company, a “Target”) trades after a proposed acquisition of such Target is announced and the value (cash plus stock) that the acquiring company (the “Acquirer”) has proposed to pay for the stock of the Target (a “Spread”). Such a Spread typically exists due to the uncertainty that the announced merger, acquisition or other corporate reorganization (each, a “Deal”) will close, and if it closes, that such Deal will be at the initially proposed economic terms. For Deals that close, the price of the Target after the Deal is announced is expected to approach the proposed acquisition price by the closing date of the Deal, resulting in a gain to strategies such as the Index’s, which attempt to capture this Spread. The size of the Spread will depend on several factors, including the perceived risk of the Deal closing and the length of time expected until the Deal is completed. For Deals that are not consummated, the price of the Target commonly falls back to pre-announcement levels, typically resulting in significant losses well in excess of the post-announcement Spread the strategy attempts to capture.

To obtain exposure to the Index, the Fund takes long positions in shares of the Target. The Fund also takes short positions in shares of the Acquirer when the Deal involves an exchange of the Acquirer’s stock. The short positions are intended to reduce the effect that declines in the value of the Acquirer’s stock could have on the Spread.

The Index, created by Standard & Poor’s®, provides exposure to up to 40 publicly announced Deals within developed market countries through a combination of long and, in certain cases, short security positions. When Deals enter the Index, the weight in long positions of Targets is initiated at three percent (3%) and the initial weight in short positions of Acquirers ranges between zero and three percent (0% and 3%), depending on terms of the Deal. The sum of initial net exposure for the Fund (i.e., the difference between: (a) the Fund’s total long exposure; and (b) the Fund’s total short exposure) is limited to between zero and one hundred percent (0% and 100%), with both the long and short positions having a maximum initial exposure each of 120%. The Index also includes a Treasury bill component which constitutes the remainder of the Index when net exposure from included Deals is less than 100%. Certain Deals are screened out based on liquidity, size, and Spread between the Deal price and the Target’s stock price following the announcement of the Deal. Additions and deletions occur on a rolling basis.

The Index is denominated in local currencies, and the Fund will generally seek to hedge against the impact of currency movements.

For a further description of the Index, please see “Description of the S&P Merger Arbitrage Index” in the Fund’s full Prospectus.

The Fund invests in a combination of equity securities and derivatives that ProShare Advisors believes, in combination, should track the performance of the Index. Under normal circumstances, the Fund will invest at least 80% of its total assets in component securities (i.e., securities of the Index and comparable securities that have economic characteristics that are substantially identical to the economic characteristics of the securities of the Index). The Fund will generally not short any stocks directly but will generally obtain short exposure through derivaties. The types of securities and derivatives that the Fund will principally invest in are set forth below. Cash balances arising from the use of derivatives will typically be held in money market instruments.

• Equity Securities — The Fund invests in common stock issued by U.S. and foreign public companies.

• Derivatives — The Fund invests in derivatives, which are financial instruments whose value is derived from the value of an underlying asset, exchange rate, interest rate or index. The Fund invests in derivatives as a substitute for investing directly in or making short sales of the securities of the Index, as well as for effecting currency hedging transactions. These derivatives principally include:

• Swap Agreements — Contracts entered into primarily with major global financial institutions for a specified period ranging from a day to more than one year. In a standard “swap” transaction, two parties agree to exchange the return (or differentials in rates of return) earned or realized on particular predetermined investments or instruments. The gross return to be exchanged or “swapped” between the parties is calculated with respect to a “notional amount,” e.g., the return on or change in value of a particular dollar amount invested in a “basket” of securities representing a particular index.

• Forward Contracts — Two-party contracts where a purchase or sale of a specific quantity of a commodity, security, foreign currency or other financial instrument is entered into with dealers or financial institutions at a set price, with delivery and settlement at a specified future date. Forward contracts may also be structured for cash settlement, rather than physical delivery.

• Money Market Instruments — The Fund invests in short-term cash instruments that have a remaining maturity of 397 days or less and exhibit high quality credit profiles, including:

• U.S. Treasury Bills — U.S. government securities that have initial maturities of one year or less, and are supported by the full faith and credit of the United States.

• Repurchase Agreements — Contracts in which a seller of securities, usually U.S. government securities or other money market instruments, agrees to buy them back at a specified time and price. Repurchase agreements are primarily used by the Fund as a short-term investment vehicle for cash positions.

ProShare Advisors uses a mathematical approach to investing. Using this approach, ProShare Advisors determines the type, quantity and mix of investment positions that the Fund should hold to approximate the performance of the Index. The Fund may gain exposure to only a representative sample of the securities in the Index, which exposure is intended to have aggregate characteristics similar to those of the Index, and may invest in securities or financial instruments not contained in the Index. ProShare Advisors does not invest the assets of the Fund in securities or derivatives based on ProShare Advisors’ view of the investment merit of a particular security, instrument, or company, other than for cash management purposes, nor does it conduct conventional research or analysis (other than in determining counterparty creditworthiness), or forecast market movement or trends, in managing the assets of the Fund. The Fund seeks to remain fully invested at all times in securities and/or derivatives that, in combination, provide exposure to the Index without regard to market conditions, trends or direction.

Please see “Investment Objective, Principal Investment Strategies and Related Risks” in the Fund’s full Prospectus for additional details.

Principal Risks

You could lose money by investing in the Fund.

• Risks Associated with the Use of Derivatives — The Fund uses investment techniques and derivatives that may be considered aggressive. Investing in derivatives may expose the Fund to greater risks than investing directly in the reference asset(s) underlying those derivatives, such as counterparty risk, liquidity risk and increased correlation risk (each as discussed below). When the Fund uses derivatives, there may be imperfect correlation between the value of the reference asset(s) and the derivative, which may prevent the Fund from achieving its investment objective. Moreover, with respect to the use of swap agreements, if the Index has a dramatic intraday move that causes a material decline in the Fund’s net assets, the terms of a swap agreement between the Fund and its counterparty may permit the counterparty to immediately close out the transaction with the Fund. In that event, the Fund may be unable to enter into another swap agreement or invest in other derivatives to achieve the desired exposure consistent with the Fund’s investment objective. This, in turn, may prevent the Fund from achieving its investment objective, even if the Index reverses all or a portion of its intraday move by the end of the day. Any financing, borrowing and other costs associated with using derivatives may also have the effect of lowering the Fund’s return.

• Correlation Risk — A number of factors may affect the Fund’s ability to achieve a high degree of correlation with the Index, and there can be no guarantee that the Fund will achieve a high degree of correlation. Failure to achieve a high degree of correlation may prevent the Fund from achieving its investment objective. The factors that may adversely affect the Fund’s correlation with the Index, include fees, expenses, transaction costs, financing costs associated with the use of derivatives, income items, valuation methodology, accounting standards and disruptions or illiquidity in the markets for the securities or financial instruments in which the Fund invests. The Fund may not have investment exposure to all securities in the Index, or its weighting of investment exposure to such securities may be different from that of the Index. In addition, the Fund may invest in securities or financial instruments not included in the Index. The Fund may also be subject to large movements of assets into and out of the Fund, potentially resulting in the Fund being over- or under-exposed to the Index. Activities surrounding Index reconstitutions and other Index rebalancing events may hinder the Fund’s ability to meet its investment objective. The Fund’s foreign currency hedging strategy may also be unable to perfectly match the Index and will introduce additional costs, both sources of additional correlation risk.

• Risks Related to Foreign Currencies and the Fund’s Currency Hedging Strategy — The Index is denominated in local currencies and does not reflect the impact of currency movements that can effect U.S. investors (such as the Fund) in such securities. The Fund will generally attempt to match the Index by hedging against exposure to foreign currencies. These hedges will in many cases not fully eliminate the exposure to a particular currency. In addition, interest rate differentials and additional transaction costs can diminish the effectiveness of a particular hedging position. All of these factors may cause additional correlation risk.

• Exposure to Foreign Investments Risk — Exposure to securities of foreign issuers may provide the Fund with increased risk. Various factors related to foreign investments may negatively impact the Index’s performance, such as: i) fluctuations in the value of the local currency versus the U.S. dollar and the uncertainty associated with the cost of converting between various currencies even if the Fund attempts to hedge against its currency exposure; ii) differences in securities settlement practices; iii) uncertainty associated with evidence of ownership of investments in countries that lack centralized custodial services; iv) possible regulation of, or other limitations on, investments by U.S. investors in foreign investments; v) potentially higher brokerage commissions; vi) the possibility that a foreign government may withhold portions of interest and dividends at the source; vii) taxation of income earned in foreign countries or other foreign taxes imposed; viii) foreign exchange controls, which may include suspension of the ability to transfer currency from a foreign country; ix) less publicly available information about foreign issuers; x) changes in the denomination currency of a foreign investment; and xi) less certain legal systems in which the Fund might encounter difficulties or be unable to pursue legal remedies. Foreign investments also may be more susceptible to political, social, economic and regional factors than might be the case with U.S. securities.

• Risks Related to the Merger Arbitrage Strategy — The Fund is subject to the risks associated with the transactions targeted by the Index generally to the same extent as its underlying Index is so exposed. There is no assurance that any of the Deals reflected in the Index will be successfully completed. In particular, in certain market conditions, it is possible that most or all of the Deals could fail. If any Deal reflected in the Index is not consummated, the Spread between the price offered for the Target and the price at which the shares of the Target trade is expected to widen. In such cases the price of the Target commonly falls back to pre-Deal announcement levels, typically resulting in significant losses well in excess of the post-announcement Spread the strategy attempts to capture. This could adversely affect the performance of the Index and the performance of the Fund. Deals may be terminated, renegotiated, or subject to a longer time frame than initially contemplated due to business, regulatory, or other concerns. Any of these events may negatively impact the performance of the Fund. The Index may also delete transactions under certain circumstances, thus precluding any potential future gains. Also, foreign companies involved in pending mergers or acquisitions may present risks distinct from comparable transactions completed solely within the U.S.

• Long/Short Risk — The Fund seeks long exposure to certain securities and short exposure to certain other securities. There is no guarantee that the returns on the Fund’s long or short positions will produce high, or even positive, returns and the Fund could lose money if either or both the Fund’s long and short positions produce negative returns.

• Short Sale Exposure Risk — The Fund may seek inverse exposure through financial instruments such as swap agreements, which may cause the Fund to be exposed to certain risks associated with selling securities short. These risks include, under certain market conditions, the cost of shorting securities, which is not reflected in the Index, an increase in the volatility and decrease in the liquidity of securities underlying the short position, which may adversely impact the Fund’s return, result in a loss, have the effect of limiting the Fund’s ability to obtain inverse exposure through financial instruments such as swap agreements, or require the Fund to seek inverse exposure through alternative investment strategies that may be less desirable or may be costly to implement. To the extent that, at any particular point in time, the securities underlying the short position may be thinly traded or have a limited market, including due to regulatory action, the Fund may be unable to meet its investment objective due to a lack of a counterparty or counterparties. During such periods, the Fund’s ability to issue additional Creation Units may be adversely affected. Obtaining inverse exposure through these instruments may be considered an aggressive investment technique. The Fund may not have exposure to all short components of the Index or may have short exposure to securities not included in the Index.

• Counterparty Risk — The Fund will be subject to credit risk (i.e., the risk that a counterparty is unwilling or unable to make timely payments to meet its contractual obligations) with respect to the amount it expects to receive from counterparties to derivatives or repurchase agreements entered into by the Fund. If a counterparty becomes bankrupt or fails to perform its obligations, the value of your investment in the Fund may decline.

• Early Close/Late Close/Trading Halt Risk — An exchange or market may close early, close late or issue trading halts on specific securities, or the ability to buy or sell certain securities or derivatives may be restricted, which may result in the Fund being unable to buy or sell certain securities or derivatives. In such circumstances, the Fund may be unable to rebalance its portfolio, may be unable to accurately price its investments and/or may incur substantial trading losses.

• Equity and Market Risk — The equity markets are volatile, and the value of securities, swaps, and other instruments correlated with the equity markets may fluctuate dramatically from day-to-day. Equity markets are subject to political, regulatory, market and economic developments, as well as developments that impact specific economic sectors, industries or segments of the market. Volatility in the markets and/or adverse market developments may cause the value of an investment in the Fund to decrease.

• Index Performance Risk — There is no guarantee or assurance that the methodology used to create the Index will result in the Fund achieving high, or even positive, returns. The Index may underperform more traditional indices. In turn, the Fund could lose value while other indices or measures of market performance increase in value.

• Liquidity Risk — In certain circumstances, such as the disruption of the orderly markets for the securities or derivatives in which the Fund invests, the Fund might not be able to dispose of certain holdings quickly or at prices that represent true market value in the judgment of ProShare Advisors. Markets for the securities or derivatives in which the Fund invests may be disrupted by a number of events, including but not limited to economic crises, natural disasters, new legislation, or regulatory changes inside or outside of the U.S. For example, regulation limiting the ability of certain financial institutions to invest in certain securities would likely reduce the liquidity of those securities. Such situations may prevent the Fund from limiting losses, realizing gains or achieving a high correlation with the Index.

• Market Price Variance Risk — Fund shares are listed for trading on the BATS Exchange and can be bought and sold in the secondary market at market prices. The market prices of shares will fluctuate in response to changes in net asset value (“NAV”) and supply and demand for shares. ProShare Advisors cannot predict whether shares will trade above, below or at their NAV. Given the fact that shares can be created and redeemed in Creation Units, as defined below, ProShare Advisors believes that large discounts or premiums to the NAV of shares should not be sustained. The Fund’s investment results are measured based upon the daily NAV of the Fund. Investors purchasing and selling shares in the secondary market may not experience investment results consistent with those experienced by investors creating and redeeming directly with the Fund.

• Non-Diversification Risk — The Fund is classified as “non-diversified” under the Investment Company Act of 1940, and has the ability to invest a relatively high percentage of its investments in the securities of a small number of issuers susceptible to a single economic, political or regulatory event, or in derivative instruments with a single counterparty if ProShare Advisors determines that doing so is the most efficient means of meeting the Fund’s investment objective. This makes the performance of the Fund more susceptible to adverse impact to an issuer or counterparty than a diversified fund might be. This risk may be particularly acute when the Index is comprised of a small number of securities.

• Portfolio Turnover Risk — Active market trading of the Fund’s shares may cause more frequent creation or redemption activities that could, in certain circumstances, increase the number of portfolio transactions. High levels of transactions increase brokerage costs and may result in increased taxable capital gains.

• Valuation Risk — In certain circumstances, portfolio securities may be valued using techniques other than market quotations. The value established for a portfolio security may be different from what would be produced through the use of another methodology or if it had been priced using market quotations. Portfolio securities that are valued using techniques other than market quotations, including “fair valued” securities, may be subject to greater fluctuation in their value from one day to the next than would be the case if market quotations were used. In addition, there is no assurance that the Fund could sell a portfolio security for the value established for it at any time, and it is possible that the Fund would incur a loss because a portfolio security is sold at a discount to its established value.

Investment Results

After the Fund has a full calendar year of performance information, performance information will be shown on an annual basis. Annual returns are required to be shown and should not be interpreted as suggesting that the Fund should or should not be held for longer periods of time. The Fund may not be suitable for all investors.

[1] "Other Expenses" are based on estimated amounts for the current fiscal year.

[2] ProShare Advisors LLC ("ProShare Advisors" or the "Advisor") has contractually agreed to waive Investment Advisory and Management Services Fees and to reimburse Other Expenses to the extent Total Annual Fund Operating Expenses Before Fee Waivers and Expense Reimbursements, as a percentage of average daily net assets, exceed 0.75% through September 30, 2014. After such date, the expense limitation may be terminated or revised. Amounts waived or reimbursed in a particular contractual period may be recouped by ProShare Advisors within five years of the end of that contractual period to the extent that recoupment will not cause the Fund's expenses to exceed any expense limitation in place at that time.

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	PROSHARES TRUST
Prospectus Date	rr_ProspectusDate	Dec. 10, 2012
Document Creation Date	dei_DocumentCreationDate	Dec. 06, 2012

XML

Document and Entity Information	12 Months Ended
	Dec. 10, 2012
Risk/Return:
Document Type	485BPOS
Document Period End Date	Dec. 06, 2012
Registrant Name	PROSHARES TRUST
Central Index Key	0001174610
Amendment Flag	false
Document Creation Date	Dec. 06, 2012
Document Effective Date	Dec. 06, 2012
Prospectus Date	Dec. 10, 2012

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	PROSHARES TRUST
Prospectus Date	rr_ProspectusDate	Dec. 10, 2012
ProShares Merger ETF
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	ProShares Merger ETF
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	ProShares Merger ETF (the “Fund”) seeks investment results, before fees and expenses, that track the performance of the S&P Merger Arbitrage Index (the “Index”).
Expense [Heading]	rr_ExpenseHeading	Fees and Expenses of the Fund
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	The table below describes the fees and expenses that you may pay if you buy or hold shares of the Fund.
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	September 30, 2014
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the example above, affect the Fund’s performance. The Fund’s portfolio turnover rate is calculated without regard to cash instrument or derivatives transactions. If such transactions were included, the Fund’s portfolio turnover rate would be significantly higher. Although the Fund has not yet commenced operations as of the date of this Prospectus and no portfolio turnover information is provided for this Fund, the Fund expects its portfolio turnover rate to exceed 100%.
Other Expenses, New Fund, Based on Estimates [Text]	rr_OtherExpensesNewFundBasedOnEstimates	“Other Expenses” are based on estimated amounts for the current fiscal year.
Expense Example [Heading]	rr_ExpenseExampleHeading	Example:
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	This example is intended to help you compare the cost of investing in the Fund with the cost of investing in other funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of each period. The example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same, except that the fee waiver/expense reimbursement is assumed only to pertain to the first year. Although your actual cost may be higher or lower, based on these assumptions your approximate costs would be:
Expense Example Closing [Text Block]	rr_ExpenseExampleClosingTextBlock	The Fund pays transaction and financing costs associated with transacting in securities and derivatives. In addition, investors may pay brokerage commissions on their purchases and sales of the Fund’s shares. These costs are not reflected in the example or the table above.
Strategy [Heading]	rr_StrategyHeading	Principal Investment Strategies
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Fund is designed to track the performance of the Index and provide exposure to a global merger arbitrage strategy, which seeks to capture the spread between the price at which the stock of a company (each such company, a “Target”) trades after a proposed acquisition of such Target is announced and the value (cash plus stock) that the acquiring company (the “Acquirer”) has proposed to pay for the stock of the Target (a “Spread”). Such a Spread typically exists due to the uncertainty that the announced merger, acquisition or other corporate reorganization (each, a “Deal”) will close, and if it closes, that such Deal will be at the initially proposed economic terms. For Deals that close, the price of the Target after the Deal is announced is expected to approach the proposed acquisition price by the closing date of the Deal, resulting in a gain to strategies such as the Index’s, which attempt to capture this Spread. The size of the Spread will depend on several factors, including the perceived risk of the Deal closing and the length of time expected until the Deal is completed. For Deals that are not consummated, the price of the Target commonly falls back to pre-announcement levels, typically resulting in significant losses well in excess of the post-announcement Spread the strategy attempts to capture. To obtain exposure to the Index, the Fund takes long positions in shares of the Target. The Fund also takes short positions in shares of the Acquirer when the Deal involves an exchange of the Acquirer’s stock. The short positions are intended to reduce the effect that declines in the value of the Acquirer’s stock could have on the Spread. The Index, created by Standard & Poor’s®, provides exposure to up to 40 publicly announced Deals within developed market countries through a combination of long and, in certain cases, short security positions. When Deals enter the Index, the weight in long positions of Targets is initiated at three percent (3%) and the initial weight in short positions of Acquirers ranges between zero and three percent (0% and 3%), depending on terms of the Deal. The sum of initial net exposure for the Fund (i.e., the difference between: (a) the Fund’s total long exposure; and (b) the Fund’s total short exposure) is limited to between zero and one hundred percent (0% and 100%), with both the long and short positions having a maximum initial exposure each of 120%. The Index also includes a Treasury bill component which constitutes the remainder of the Index when net exposure from included Deals is less than 100%. Certain Deals are screened out based on liquidity, size, and Spread between the Deal price and the Target’s stock price following the announcement of the Deal. Additions and deletions occur on a rolling basis. The Index is denominated in local currencies, and the Fund will generally seek to hedge against the impact of currency movements. For a further description of the Index, please see “Description of the S&P Merger Arbitrage Index” in the Fund’s full Prospectus. The Fund invests in a combination of equity securities and derivatives that ProShare Advisors believes, in combination, should track the performance of the Index. Under normal circumstances, the Fund will invest at least 80% of its total assets in component securities (i.e., securities of the Index and comparable securities that have economic characteristics that are substantially identical to the economic characteristics of the securities of the Index). The Fund will generally not short any stocks directly but will generally obtain short exposure through derivaties. The types of securities and derivatives that the Fund will principally invest in are set forth below. Cash balances arising from the use of derivatives will typically be held in money market instruments. Equity Securities — The Fund invests in common stock issued by U.S. and foreign public companies. Derivatives — The Fund invests in derivatives, which are financial instruments whose value is derived from the value of an underlying asset, exchange rate, interest rate or index. The Fund invests in derivatives as a substitute for investing directly in or making short sales of the securities of the Index, as well as for effecting currency hedging transactions. These derivatives principally include: Swap Agreements — Contracts entered into primarily with major global financial institutions for a specified period ranging from a day to more than one year. In a standard “swap” transaction, two parties agree to exchange the return (or differentials in rates of return) earned or realized on particular predetermined investments or instruments. The gross return to be exchanged or “swapped” between the parties is calculated with respect to a “notional amount,” e.g., the return on or change in value of a particular dollar amount invested in a “basket” of securities representing a particular index. Forward Contracts — Two-party contracts where a purchase or sale of a specific quantity of a commodity, security, foreign currency or other financial instrument is entered into with dealers or financial institutions at a set price, with delivery and settlement at a specified future date. Forward contracts may also be structured for cash settlement, rather than physical delivery. Money Market Instruments — The Fund invests in short-term cash instruments that have a remaining maturity of 397 days or less and exhibit high quality credit profiles, including: U.S. Treasury Bills — U.S. government securities that have initial maturities of one year or less, and are supported by the full faith and credit of the United States. Repurchase Agreements — Contracts in which a seller of securities, usually U.S. government securities or other money market instruments, agrees to buy them back at a specified time and price. Repurchase agreements are primarily used by the Fund as a short-term investment vehicle for cash positions. ProShare Advisors uses a mathematical approach to investing. Using this approach, ProShare Advisors determines the type, quantity and mix of investment positions that the Fund should hold to approximate the performance of the Index. The Fund may gain exposure to only a representative sample of the securities in the Index, which exposure is intended to have aggregate characteristics similar to those of the Index, and may invest in securities or financial instruments not contained in the Index. ProShare Advisors does not invest the assets of the Fund in securities or derivatives based on ProShare Advisors’ view of the investment merit of a particular security, instrument, or company, other than for cash management purposes, nor does it conduct conventional research or analysis (other than in determining counterparty creditworthiness), or forecast market movement or trends, in managing the assets of the Fund. The Fund seeks to remain fully invested at all times in securities and/or derivatives that, in combination, provide exposure to the Index without regard to market conditions, trends or direction. Please see “Investment Objective, Principal Investment Strategies and Related Risks” in the Fund’s full Prospectus for additional details.
Risk [Heading]	rr_RiskHeading	Principal Risks
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	You could lose money by investing in the Fund. Risks Associated with the Use of Derivatives — The Fund uses investment techniques and derivatives that may be considered aggressive. Investing in derivatives may expose the Fund to greater risks than investing directly in the reference asset(s) underlying those derivatives, such as counterparty risk, liquidity risk and increased correlation risk (each as discussed below). When the Fund uses derivatives, there may be imperfect correlation between the value of the reference asset(s) and the derivative, which may prevent the Fund from achieving its investment objective. Moreover, with respect to the use of swap agreements, if the Index has a dramatic intraday move that causes a material decline in the Fund’s net assets, the terms of a swap agreement between the Fund and its counterparty may permit the counterparty to immediately close out the transaction with the Fund. In that event, the Fund may be unable to enter into another swap agreement or invest in other derivatives to achieve the desired exposure consistent with the Fund’s investment objective. This, in turn, may prevent the Fund from achieving its investment objective, even if the Index reverses all or a portion of its intraday move by the end of the day. Any financing, borrowing and other costs associated with using derivatives may also have the effect of lowering the Fund’s return. Correlation Risk — A number of factors may affect the Fund’s ability to achieve a high degree of correlation with the Index, and there can be no guarantee that the Fund will achieve a high degree of correlation. Failure to achieve a high degree of correlation may prevent the Fund from achieving its investment objective. The factors that may adversely affect the Fund’s correlation with the Index, include fees, expenses, transaction costs, financing costs associated with the use of derivatives, income items, valuation methodology, accounting standards and disruptions or illiquidity in the markets for the securities or financial instruments in which the Fund invests. The Fund may not have investment exposure to all securities in the Index, or its weighting of investment exposure to such securities may be different from that of the Index. In addition, the Fund may invest in securities or financial instruments not included in the Index. The Fund may also be subject to large movements of assets into and out of the Fund, potentially resulting in the Fund being over- or under-exposed to the Index. Activities surrounding Index reconstitutions and other Index rebalancing events may hinder the Fund’s ability to meet its investment objective. The Fund’s foreign currency hedging strategy may also be unable to perfectly match the Index and will introduce additional costs, both sources of additional correlation risk. Risks Related to Foreign Currencies and the Fund’s Currency Hedging Strategy — The Index is denominated in local currencies and does not reflect the impact of currency movements that can effect U.S. investors (such as the Fund) in such securities. The Fund will generally attempt to match the Index by hedging against exposure to foreign currencies. These hedges will in many cases not fully eliminate the exposure to a particular currency. In addition, interest rate differentials and additional transaction costs can diminish the effectiveness of a particular hedging position. All of these factors may cause additional correlation risk. Exposure to Foreign Investments Risk — Exposure to securities of foreign issuers may provide the Fund with increased risk. Various factors related to foreign investments may negatively impact the Index’s performance, such as: i) fluctuations in the value of the local currency versus the U.S. dollar and the uncertainty associated with the cost of converting between various currencies even if the Fund attempts to hedge against its currency exposure; ii) differences in securities settlement practices; iii) uncertainty associated with evidence of ownership of investments in countries that lack centralized custodial services; iv) possible regulation of, or other limitations on, investments by U.S. investors in foreign investments; v) potentially higher brokerage commissions; vi) the possibility that a foreign government may withhold portions of interest and dividends at the source; vii) taxation of income earned in foreign countries or other foreign taxes imposed; viii) foreign exchange controls, which may include suspension of the ability to transfer currency from a foreign country; ix) less publicly available information about foreign issuers; x) changes in the denomination currency of a foreign investment; and xi) less certain legal systems in which the Fund might encounter difficulties or be unable to pursue legal remedies. Foreign investments also may be more susceptible to political, social, economic and regional factors than might be the case with U.S. securities. Risks Related to the Merger Arbitrage Strategy — The Fund is subject to the risks associated with the transactions targeted by the Index generally to the same extent as its underlying Index is so exposed. There is no assurance that any of the Deals reflected in the Index will be successfully completed. In particular, in certain market conditions, it is possible that most or all of the Deals could fail. If any Deal reflected in the Index is not consummated, the Spread between the price offered for the Target and the price at which the shares of the Target trade is expected to widen. In such cases the price of the Target commonly falls back to pre-Deal announcement levels, typically resulting in significant losses well in excess of the post-announcement Spread the strategy attempts to capture. This could adversely affect the performance of the Index and the performance of the Fund. Deals may be terminated, renegotiated, or subject to a longer time frame than initially contemplated due to business, regulatory, or other concerns. Any of these events may negatively impact the performance of the Fund. The Index may also delete transactions under certain circumstances, thus precluding any potential future gains. Also, foreign companies involved in pending mergers or acquisitions may present risks distinct from comparable transactions completed solely within the U.S. Long/Short Risk — The Fund seeks long exposure to certain securities and short exposure to certain other securities. There is no guarantee that the returns on the Fund’s long or short positions will produce high, or even positive, returns and the Fund could lose money if either or both the Fund’s long and short positions produce negative returns. Short Sale Exposure Risk — The Fund may seek inverse exposure through financial instruments such as swap agreements, which may cause the Fund to be exposed to certain risks associated with selling securities short. These risks include, under certain market conditions, the cost of shorting securities, which is not reflected in the Index, an increase in the volatility and decrease in the liquidity of securities underlying the short position, which may adversely impact the Fund’s return, result in a loss, have the effect of limiting the Fund’s ability to obtain inverse exposure through financial instruments such as swap agreements, or require the Fund to seek inverse exposure through alternative investment strategies that may be less desirable or may be costly to implement. To the extent that, at any particular point in time, the securities underlying the short position may be thinly traded or have a limited market, including due to regulatory action, the Fund may be unable to meet its investment objective due to a lack of a counterparty or counterparties. During such periods, the Fund’s ability to issue additional Creation Units may be adversely affected. Obtaining inverse exposure through these instruments may be considered an aggressive investment technique. The Fund may not have exposure to all short components of the Index or may have short exposure to securities not included in the Index. Counterparty Risk — The Fund will be subject to credit risk (i.e., the risk that a counterparty is unwilling or unable to make timely payments to meet its contractual obligations) with respect to the amount it expects to receive from counterparties to derivatives or repurchase agreements entered into by the Fund. If a counterparty becomes bankrupt or fails to perform its obligations, the value of your investment in the Fund may decline. Early Close/Late Close/Trading Halt Risk — An exchange or market may close early, close late or issue trading halts on specific securities, or the ability to buy or sell certain securities or derivatives may be restricted, which may result in the Fund being unable to buy or sell certain securities or derivatives. In such circumstances, the Fund may be unable to rebalance its portfolio, may be unable to accurately price its investments and/or may incur substantial trading losses. Equity and Market Risk — The equity markets are volatile, and the value of securities, swaps, and other instruments correlated with the equity markets may fluctuate dramatically from day-to-day. Equity markets are subject to political, regulatory, market and economic developments, as well as developments that impact specific economic sectors, industries or segments of the market. Volatility in the markets and/or adverse market developments may cause the value of an investment in the Fund to decrease. Index Performance Risk — There is no guarantee or assurance that the methodology used to create the Index will result in the Fund achieving high, or even positive, returns. The Index may underperform more traditional indices. In turn, the Fund could lose value while other indices or measures of market performance increase in value. Liquidity Risk — In certain circumstances, such as the disruption of the orderly markets for the securities or derivatives in which the Fund invests, the Fund might not be able to dispose of certain holdings quickly or at prices that represent true market value in the judgment of ProShare Advisors. Markets for the securities or derivatives in which the Fund invests may be disrupted by a number of events, including but not limited to economic crises, natural disasters, new legislation, or regulatory changes inside or outside of the U.S. For example, regulation limiting the ability of certain financial institutions to invest in certain securities would likely reduce the liquidity of those securities. Such situations may prevent the Fund from limiting losses, realizing gains or achieving a high correlation with the Index. Market Price Variance Risk — Fund shares are listed for trading on the BATS Exchange and can be bought and sold in the secondary market at market prices. The market prices of shares will fluctuate in response to changes in net asset value (“NAV”) and supply and demand for shares. ProShare Advisors cannot predict whether shares will trade above, below or at their NAV. Given the fact that shares can be created and redeemed in Creation Units, as defined below, ProShare Advisors believes that large discounts or premiums to the NAV of shares should not be sustained. The Fund’s investment results are measured based upon the daily NAV of the Fund. Investors purchasing and selling shares in the secondary market may not experience investment results consistent with those experienced by investors creating and redeeming directly with the Fund. Non-Diversification Risk — The Fund is classified as “non-diversified” under the Investment Company Act of 1940, and has the ability to invest a relatively high percentage of its investments in the securities of a small number of issuers susceptible to a single economic, political or regulatory event, or in derivative instruments with a single counterparty if ProShare Advisors determines that doing so is the most efficient means of meeting the Fund’s investment objective. This makes the performance of the Fund more susceptible to adverse impact to an issuer or counterparty than a diversified fund might be. This risk may be particularly acute when the Index is comprised of a small number of securities. Portfolio Turnover Risk — Active market trading of the Fund’s shares may cause more frequent creation or redemption activities that could, in certain circumstances, increase the number of portfolio transactions. High levels of transactions increase brokerage costs and may result in increased taxable capital gains. Valuation Risk — In certain circumstances, portfolio securities may be valued using techniques other than market quotations. The value established for a portfolio security may be different from what would be produced through the use of another methodology or if it had been priced using market quotations. Portfolio securities that are valued using techniques other than market quotations, including “fair valued” securities, may be subject to greater fluctuation in their value from one day to the next than would be the case if market quotations were used. In addition, there is no assurance that the Fund could sell a portfolio security for the value established for it at any time, and it is possible that the Fund would incur a loss because a portfolio security is sold at a discount to its established value.
Risk Lose Money [Text]	rr_RiskLoseMoney	You could lose money by investing in the Fund.
Risk Nondiversified Status [Text]	rr_RiskNondiversifiedStatus	Non-Diversification Risk — The Fund is classified as “non-diversified” under the Investment Company Act of 1940, and has the ability to invest a relatively high percentage of its investments in the securities of a small number of issuers susceptible to a single economic, political or regulatory event, or in derivative instruments with a single counterparty if ProShare Advisors determines that doing so is the most efficient means of meeting the Fund’s investment objective. This makes the performance of the Fund more susceptible to adverse impact to an issuer or counterparty than a diversified fund might be. This risk may be particularly acute when the Index is comprised of a small number of securities.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Investment Results
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	After the Fund has a full calendar year of performance information, performance information will be shown on an annual basis. Annual returns are required to be shown and should not be interpreted as suggesting that the Fund should or should not be held for longer periods of time. The Fund may not be suitable for all investors.
Performance One Year or Less [Text]	rr_PerformanceOneYearOrLess	After the Fund has a full calendar year of performance information, performance information will be shown on an annual basis.
ProShares Merger ETF | ProShares Merger ETF
Risk/Return:	rr_RiskReturnAbstract
Investment Advisory Fees	rr_ManagementFeesOverAssets	0.75%
Other Expenses	rr_OtherExpensesOverAssets	1.36%	[1]
Total Annual Fund Operating Expenses Before Fee Waivers and Expense Reimbursements	rr_ExpensesOverAssets	2.11%
Fee Waiver/Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(1.36%)	[2]
Total Annual Fund Operating Expenses After Fee Waivers and Expense Reimbursements	rr_NetExpensesOverAssets	0.75%
1 Year	rr_ExpenseExampleYear01	77
3 Years	rr_ExpenseExampleYear03	530

[1] "Other Expenses" are based on estimated amounts for the current fiscal year.

[2] ProShare Advisors LLC ("ProShare Advisors" or the "Advisor") has contractually agreed to waive Investment Advisory and Management Services Fees and to reimburse Other Expenses to the extent Total Annual Fund Operating Expenses Before Fee Waivers and Expense Reimbursements, as a percentage of average daily net assets, exceed 0.75% through September 30, 2014. After such date, the expense limitation may be terminated or revised. Amounts waived or reimbursed in a particular contractual period may be recouped by ProShare Advisors within five years of the end of that contractual period to the extent that recoupment will not cause the Fund's expenses to exceed any expense limitation in place at that time.