Exchange operators often raise so-called margin requirements at times of large market swings.

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Margin loans may finance only 1.5% of the value of the New York Stock Exchange but prices are set by those in the market on a given day, among whom the margin men are concentrated.

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Nowadays, an exchange-traded fund can do the heavy lifting for you, no margin required.

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The markets that do the sort of high volume, low margin trades that would be affected by an FTT are the foreign exchange (FX), futures, options and stock markets (with special reference to high frequency trading of the often demonised computer algorithm type).

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What we're doing is putting together, in one margin calculation, both futures positions that are traded on New York Stock Exchange's futures exchange, NYSE Liffe US, and the fixed income securities positions that are currently cleared at DTCC FICC, the fixed income clearing corporation.

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ZeroHedge notes that the most recent hike comes two weeks after a 22% margin hike on gold by the CME and two days after the Shanghai Gold Exchange raised them by 26%.

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To hold onto the contract overnight, it's necessary to post a margin that depends on the contract's volatility and is set by the listing exchange.

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Margin requirements in the spotlight this week again after the CME Group, owner of futures exchange NYMEX, announced a 25% hike in collateral requirements for crude oil futures, putting initial, and short-lived, pressure on WTI and Brent prices.

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