In a futures market, if the price is $500/BTC, an investor needs to buy 50 futures contracts, each worth $10. If an investor wishes to open a positive position then he goes long with “buy" contracts, and if he decides to open a negative position, he goes short with “sell” contracts. An investor’s position can be either positive or negative for the same instrument. (For more, see: Bitcoin Mass Hysteria: The Disaster that Brought Down Mt. Gox.)

In contrast, if you are “going short” on Bitcoin, you assume that Bitcoin prices will fall. Buying put options will enable you to sell Bitcoin at some point in the future at a price that is higher than the future price you expect. In analogy to the example above, if the current Bitcoin price is 5,000 USD and you expect it to fall to 2,000 USD in 6 months, then put options allowing you to sell Bitcoin for 5,000 USD in 5 months (when everyone else is selling for 2000 USD) are very valuable.
Exchanges simply take a fee to facilitate the orderbook where its clients (the counterparties) create and trade futures contract with each other. They also have to manage the system's risk so that traders don't get overleveraged or manipulate the market. Since counterparties are only putting margin down that is a % of the contract value, the exchange also has to handle liquidation procedures in case the value of the margin is exceeded by the loss on the notional market value of the contract. For instance, BitMEX offers 100x leverage, so if you want to enter a $10,000 position you need to put down $100 worth of bitcoin. If the price moves just 0.5% against your favor, BitMEX will take over your position and execute it into the market, so that the person on the other side of the contract can have someone else who pays for the profit. In the event that the liquidation doesn't get passed off to another trader, an Auto-Deleveraging/Termination can occur, or Socialize Loss in the contract builds (we will discuss these issues in more detail later).
There is no registry showing which individuals or entities own bitcoin or the quantity of bitcoin that is owned by any particular person or entity. It is possible, and in fact, reasonably likely, that a small group of early bitcoin adopters hold a significant proportion of the bitcoin that has been thus far created. There are no regulations in place that would prevent a large holder of bitcoin from selling their bitcoin, which could depress the price of bitcoin and have an adverse effect on an investment in the Funds which do not take a short position in bitcoin futures contracts.
Bitcoin relies on blockchain technology. “Blockchain” is a decentralized database. Transactions are grouped in blocks and then chained together through cryptographic links. Blockchain is designed so that the chain can be added to, but not edited. This structure is called a “distributed ledger.” Transactions in the distributed ledger are permanently recorded and can never disappear, although theft and loss of bitcoin can occur. While bitcoin has grown in popularity, it’s still not nearly as widely accepted as traditional currency.
Individual shares of the Fund will be listed for trading on [the Exchange] and can be bought and sold in the secondary market at market prices. The market price of shares will fluctuate in response to changes in the value of the Fund’s holdings, supply and demand for shares, and other market factors. ProShare Advisors cannot predict whether the Fund’s shares will trade above, below or at a price equal to the value of the Fund’s holdings. Differences between secondary market prices and NAV, the value of the Fund’s holdings, may be due largely to supply and demand forces in the secondary market, which may not be the same forces as those influencing prices for securities or financial instruments held by the Fund at a particular time. Given the fact that the Fund’s shares can be created and redeemed in Creation Units, ProShare Advisors believes that large discounts or premiums to the value of the Fund’s holdings should not be sustained.
It can often be confusing to traders who are using multiple futures exchanges with different contract types -- inverse and qunato, dailies or quarterlies, 5x or 100x -- so people wonder: what should I trade? Well, it depends on what your goals are. If you are trying to do a little hedge for a medium term, you would want to use a quarterlies expiration contract instead, because otherwise you'd have to reopen shorter-term contracts after they expire and settle. 

The audited Financial Statements, for each Fund that commenced operations prior to May 31, 2017, and the report of PricewaterhouseCoopers LLP, as independent registered public accounting firm, for the fiscal year ended May 31,2017, that appear in the Annual Report to shareholders dated May 31, 2017, are hereby incorporated by reference in this SAI. The Annual Report to shareholders is delivered with this SAI to shareholders requesting this SAI.

Under normal market conditions, each Fund intends to invest substantially all of its assets in Benchmark Futures Contracts. The contractual obligations of a buyer or seller holding a futures contract to expiration may be satisfied by settling in cash as designated in the contract specifications. Alternatively, futures contracts may be closed out prior to expiration by making an offsetting sale or purchase of an identical futures contract on the same or linked exchange before the designated date of settlement. Once this date is reached, the futures contract “expires.” The Funds do not intend to hold bitcoin futures contracts through expiration, but instead to “roll” their respective positions. “Rolling” refers to a process whereby futures contracts nearing expiration are closed out and replaced with an identical futures contract with a later expiration date. Accordingly, the Funds are subjects to risks related to rolling.
Traders A and B in the previous example are hedgers. However, futures contracts, once they exist, can also be bought and sold in their own right. This is where futures get interesting for speculators. Say that Speculator X believes the price of a ton of pork belly will rise to 1,200 USD in 3 months’ time, so buying the futures contract at 1,000 USD is a good deal. He can then sell the contract to bacon producers who want to buy pork bellies at 1,000 USD. The option to buy at a specified price in the future is known as a call option. The price of call options rise when traders assume that the price of the underlying asset will rise.