Options and futures often carry higher commissions than equity trades and investors in futures will be required to maintain a minimum margin.

FORBES: Profiting From Fear With Exchange-Traded VIX Notes

They have to commit to a minimum trading volume, and a maximum margin between bid- and offer- prices.

ECONOMIST: South Korea

If Mr. Market trashes your investments in a sudden panic, your margin debts may be "called, " forcing you to sell some of your assets to sustain the minimum account values you committed to under the terms of the loan.

WSJ: The Intelligent Investor: Borrowing Against Yourself