In investing, there's an adage that posits: The best investments are often the ones you don't make.

And isn't that the truth regarding natural gas, or at least the natural gas-based fund, United States Natural Gas Fund LP (UNG)?

They don't all work out. The United States Natural Gas Fund (UNG), which I first wrote about on July 13, 2009 at a price of $11.50, has been stopped out at $8.40.

What's more, UNG, as they say, 'has not let a stop loss get in the way of a good downtrend.' In this case, make that a horrible downtrend, as UNG traded at about $7.50 on Thursday.

It's a close call, but I'm reiterating my buy rating for the United States Natural Gas Fund (UNG), first recommended on July 13, 2009, at a price of $11.50. Further, the buy call is nuanced, so attention is advised.

First, UNG, currently trading around $10.80, a low-cost way for the typical investor to invest in natural gas as a commodity, is a high-risk play: don't buy UNG if you're a moderate-risk or low-risk investor.

I'm issuing a Buy for the United States Natural Gas Fund (NYSE: UNG), but there are several qualifiers, so pay attention.

First, UNG, currently trading around $11.50, a low-cost way for the typical investor to invest in natural gas as a commodity, is a high-risk play. Don't Buy UNG if you're a moderate-risk of low-risk investor.

The United States Natural Gas Fund LP (NYSE: UNG) resumed issuing new shares Monday, ending a long drought for the exchange-traded fund (ETF). UNG, which tracks price changes in natural gas, hasn't issued new creation baskets (blocks of 10,000 units) since June, thanks in part to newly enacted position limits on the federal and exchange level.

While it's back to business as usual, traders should still proceed with caution when it comes to this commodity-based fund. UNG warned late Friday that its units are still trading at a premium to its net asset value (NAV), which could spell trouble for investors.

United States Natural Gas Fund (NYSE: UNG) closed at $11.75. The investment objective of UNG is for the changes in percentage terms of the unit's net asset value to reflect the changes in percentage terms of the price of natural gas delivered at the Henry Hub, Louisiana. Natural Gas futures are recently down .45% to 3.743 according to Bloomberg. UNG options were active on September 16 with of 222,361 contracts trading. UNG October option implied volatility of 66 is near its 26-week average according to Track Data.

Financial Select Sector (XLF) overall volatility at 39; 26-week average is 50 according to Track Data.

Option Update is provided by Stock Specialist Paul Foster of theflyonthewall.com.

What's the latest craze? The iPhone? Kindle? A super-lightweight notebook pc?

All of the above are eye-openers. But one could argue that the biggest craze is the natural gas exchanged-traded fund, the United States Natural Gas Fund (NYSE: UNG).