You could imagine the spread going the other way, though. If everyone really was clamoring to short bitcoin, and if the futures offered a more convenient way to do it than the bitcoin exchanges, then you'd expect the short sellers to pay a premium to short via futures. Instead of selling a bitcoin at $18,000 today, they'd be willing to sell a synthetic bitcoin for $17,500, paying the spread to an arbitrageur who was willing to do the actual shorting for them. But the fact that the spread is mostly positive, and that bitcoin's price has been mostly going up, suggests that the demand has mostly been for synthetic long positions, not short.

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. 
Distributions by a Fund to a shareholder that is not a “United States person” within the meaning of the Code (such a shareholder, a “foreign shareholder”) properly reported by the Fund as (1) Capital Gain Dividends, (2) short-term capital gain dividends, and (3) interest-related dividends, each as defined and subject to certain conditions described below, generally are not subject to withholding of U.S. federal income tax.
The Officers, under the supervision of the Board, manage the day-to-day operations of the Trust. One Trustee and all of the Officers of the Trust are directors, officers or employees of ProShare Advisors or Foreside Management Services, LLC. The other Trustees are Independent Trustees. The Trustees and some Officers are also directors and officers of some or all of the other funds in the Fund Complex. The Fund Complex includes all funds advised by ProShare Advisors and any funds that have an investment adviser that is an affiliated person of ProShare Advisors.

Cryptocurrency is also used in controversial settings in the form of online black markets, such as Silk Road. The original Silk Road was shut down in October 2013 and there have been two more versions in use since then. In the year following the initial shutdown of Silk Road, the number of prominent dark markets increased from four to twelve, while the amount of drug listings increased from 18,000 to 32,000.[84]

Each Fund may engage in transactions in index options listed on national securities exchanges or traded in the OTC market as an investment vehicle for the purpose of realizing the Fund’s investment objective. The exercising holder of an index option receives, instead of the asset, cash equal to the difference between the closing level of the index and the exercise price of the option. Some index options are based on a broad market index such as the Standard & Poor’s (“S&P”) 500® Index, the New York Stock Exchange, Inc. (“NYSE”) Composite Index or on a narrower index such as the Philadelphia Stock Exchange Over-the-Counter Index. Options currently are traded on the Chicago Board Options Exchange, the NYSE Amex Options and other exchanges (collectively, “Exchanges”). Purchased OTC options and the cover for written OTC options will be subject to the relevant Fund’s 15% limitation on investment in illiquid securities. See “Illiquid Securities” below. When required by law, a Fund will segregate liquid assets in an amount equal to the value of the Fund’s total assets committed to the consummation of such options. Obligations under options so covered will not be considered senior securities for purposes of a Fund’s investment restriction concerning senior securities.

Certain Funds expect to invest in exchange-traded funds, including exchange-traded funds registered under the 1940 Act (“Underlying ETFs”). Some such Underlying ETFs will be treated as regulated investment companies for federal income tax purposes (each such Underlying ETF, an “Underlying RIC”). In such cases, a Fund’s income and gains will normally consist, in whole or part, of dividends and other distributions from the Underlying RICs and gains and losses on the disposition of shares of the Underlying RICs. The amount of income and capital gains realized by a Fund and in turn a Fund’s shareholders in respect of the Fund’s investments in Underlying RICs may be greater than such amounts would have been had the Fund invested directly in the investments held by the Underlying RICs, rather than in the shares of the Underlying RICs. Similarly, the character of such income and gains (e.g., long-term capital gain, eligibility for the dividends-received deduction, etc.) will not necessarily be the same as it would have been had the Fund invested directly in the investments held by the Underlying RICs.
The foregoing discussion is primarily a summary of certain U.S. federal income tax consequences of investing in a Fund based on the law in effect as of the date of this SAI. The discussion does not address in detail special tax rules applicable to certain classes of investors, such as, among others, IRAs and other retirement plans, tax-exempt entities, foreign investors, insurance companies, banks and other financial institutions, and investors making in-kind contributions to a Fund. Such shareholders may be subject to U.S. tax rules that differ significantly from those summarized above. You should consult your tax advisor for more information about your own tax situation, including possible other federal, state, local and, where applicable, foreign tax consequences of investing in a Fund.
I under-performed the market in 2017. A crypto market that went up several hundred percent and having read 24 books on finance and trading throughout the process, these were my biggest takeaways. Remember, these are notes I wrote to myself, so they may not work for your trading style. This version was summarized exclusively for CryptoMarket360 – a full version is hyperlinked at the bottom.
A Bitcoin futures contract is exactly what you would expect from the example above, replacing pork bellies with Bitcoin. It is a contract that enables you to buy Bitcoin at a predetermined price at a specific point in the future. For example, if today’s Bitcoin price is 8,000 USD per BTC and you expect it to rise to 10,000 USD per BTC in 4 weeks, then entering a contract which allows you to buy Bitcoin at 9,000 USD in 4 weeks is highly attractive.
In certain circumstances, the securities delivery cycles currently practicable for transferring portfolio securities to redeeming investors, coupled with foreign market holiday schedules, will require a delivery process longer than seven calendar days. The holidays applicable to various countries during such periods are listed below, as are instances where more than seven days will be needed to deliver redemption proceeds. Although certain holidays may occur on different dates in subsequent years, the number of days required to deliver redemption proceeds in any given year is not expected to exceed the maximum number of days listed below for each Fund. The proclamation of new holidays, the treatment by market participants of certain days as “informal holidays” (e.g., days on which no or limited securities transactions occur, as a result of substantially shortened trading hours), the elimination of existing holidays, or changes in local securities delivery practices, could affect the information set forth herein.
Each of the Funds may enter into repurchase agreements with financial institutions in pursuit of its investment objectives, as “cover” for the investment techniques it employs, or for liquidity purposes. Under a repurchase agreement, a Fund purchases a debt security and simultaneously agrees to sell the security back to the seller at a mutually agreed-upon future price and date, normally one day or a few days later. The resale price is greater than the purchase price, reflecting an agreed-upon market interest rate during the purchaser’s holding period. While the maturities of the underlying securities in repurchase transactions may be more than one year, the term of each repurchase agreement will always be less than one year. The Funds follow certain procedures designed to minimize the risks inherent in such agreements. These procedures include effecting repurchase transactions generally with major global financial institutions. The creditworthiness of each of the firms that is a party to a repurchase agreement with the Funds will be monitored by the Advisor. In addition, the value of the collateral underlying the repurchase agreement will always be at least equal to the repurchase price, including any accrued interest earned on the repurchase agreement. In the event of a default or bankruptcy by a selling financial institution, a Fund will seek to liquidate such collateral which could involve certain costs or delays and, to the extent that proceeds from any sale upon a default of the obligation to repurchase were less than the repurchase price, the Fund could suffer a loss. A Fund also may experience difficulties and incur certain costs in exercising its rights to the collateral and may lose the interest the Fund expected to receive under the repurchase agreement. Repurchase agreements usually are for short periods, such as one week or less, but may be longer. It is the current policy of the Funds not to invest in repurchase agreements that do not mature within seven days if any such investment, together with any other illiquid assets held by the Fund, amounts to more than 15% of the Fund’s total net assets. The investments of each of the Funds in repurchase agreements at times may be substantial when, in the view of the Advisor, liquidity, investment, regulatory, or other considerations so warrant.
Knowing their estimated costs and profit requirements the arbitrageur determines a minimum difference they need between the futures’ prices and the spot price before they will enter the market. They then monitor the price difference between Bitcoin futures and the Bitcoin exchanges and if large enough they act to profit on that gap.  For example, if a specific Bitcoin future (e.g., February contract) is trading sufficiently higher than the current Bitcoin exchange price they will short that Bitcoin future and hedge their position by buying Bitcoins on the exchange. At that point, if they have achieved trade prices within their targets, they have locked in a guaranteed profit. They will hold those positions until contract expiration (or until they can cover their short futures and sell Bitcoins at a profit).
Jordan Kelley, founder of Robocoin, launched the first bitcoin ATM in the United States on 20 February 2014. The kiosk installed in Austin, Texas is similar to bank ATMs but has scanners to read government-issued identification such as a driver's license or a passport to confirm users' identities.[60] By September 2017, 1,574 bitcoin ATMs had been installed around the world with an average fee of 9.05%. An average of 3 bitcoin ATMs were being installed per day in September 2017.[61]
Commodity Swaps. Commodity swaps are used either as substitutes for owning a specific physical commodities or as a means of obtaining non-leveraged exposure in markets where a specific commodity is not available. Commodity swaps provide the Fund with the additional flexibility of gaining exposure to commodities by using the most cost-effective vehicle available.

Margin Call - when you run out of bitcoin on your account to cover the contract positions you have taken (your account value doesn't cover the Maintance Margin) you are officially rekt. Some exchanges like CryptoFacilities will merely notify you that you have to deposit more or reduce your positions to increase your margin. Others like BitMEX will liquidate you at this level where the exchange takes over your position to liquidate it into the market to prevent system loss.
Investment income and gains received by a Fund from foreign investments may be subject to foreign withholding and other taxes, which could decrease the Fund’s return on those investments. The effective rate of foreign taxes to which a Fund will be subject depends on the specific countries in which its assets will be invested and the extent of the assets invested in each such country and, therefore, cannot be determined in advance. If more than 50% of a Fund’s assets at year end consists of the securities of foreign corporations, the Fund may elect to permit shareholders to claim a credit or deduction on their income tax returns for their pro rata portions of qualified taxes paid by the Fund to foreign countries in respect of foreign securities that the Fund has held for at least the minimum period specified in the Code. In such a case, shareholders will include in gross income from foreign sources their pro rata shares of such taxes paid by the Fund. A shareholder’s ability to claim an offsetting foreign tax credit or deduction in respect of foreign taxes paid by the Fund is subject to certain limitations imposed by the Code, which may result in the shareholder’s not receiving a full credit or deduction (if any) for the amount of such taxes. Shareholders who do not itemize on their U.S. federal income tax returns may claim a credit (but not a deduction) for such foreign taxes. Even if a Fund were eligible to make such an election for a given year, it may determine not to do so. Shareholders that are not subject to U.S. federal income tax, and those who invest in a Fund through tax-advantaged accounts (including those who invest through individual retirement accounts or other tax-advantaged retirement plans), generally will receive no benefit from any tax credit or deduction passed through by the Fund.
A Bitcoin futures contract is exactly what you would expect from the example above, replacing pork bellies with Bitcoin. It is a contract that enables you to buy Bitcoin at a predetermined price at a specific point in the future. For example, if today’s Bitcoin price is 8,000 USD per BTC and you expect it to rise to 10,000 USD per BTC in 4 weeks, then entering a contract which allows you to buy Bitcoin at 9,000 USD in 4 weeks is highly attractive.