Forex

Nearly a third of the 30 or so ETNs have been introduced this year. They include BearLinx Alerian MLP Select Index (BSR, news, msgs), which allows you to lay down a bet beside the biggest master limited partnerships in the oil patch; DB Gold Double Long (DGP, news, msgs), which gives you two times any rise in the price of gold; and Opta LBCI Pure Beta Agriculture Total Return (EOH, news, msgs), which opens a tax-deferred door to the nation's granary.

The tax breaks are under attack from the fund industry, which wants them stricken and has gotten a bill to do that introduced in the House of Representatives. The ETN industry turns that argument on its head, calling the House bill a tax increase and threatening to throw the weight of Wall Street against it.

Though the ETN market is small, it's growing. And private contracts structured the same way constitute a marketplace worth hundreds of billions of dollars.

"Tax increases of this magnitude are quite controversial," warns Shahira Knight, the managing director of the Securities Industry and Financial Markets Association