America's growing technology and unconventional reserves will give it an edge in the market, and allow it to become a gas exporter to meet rising demand.

World liquefaction capacity is growing, so that will support demand in other markets.

Focus for a moment on the source of natural gas in the future. As with oil, natural gas reserves are getting more complicated and scarcer, the so-called unconventional sources mentioned above. The more difficult and scarcer the supply becomes, the more expensive it becomes. That's another catalyst for higher prices.

Now, having told you all that, I need to pull the rug out from under you by mentioning that all of the above factors are applicable in the longer term. In the short term, I find that supply is brimming and demand is weak. That's the reason natural gas prices are low.

It's not hard to see why. Look at the recent economic figures we've received. Factories aren't exactly humming these days. Just last week, we saw another report showing that capacity utilization is still falling. The economy doesn't need as much natural gas in slow times, and these are slow times. That's why supplies are currently near peak levels.

There are two ETFs for betting on a rising natural gas price. One is UNG, which is run by the same shop that runs USO for oil, and is a vehicle based on the price of natural gas directly. An indirect approach is also available via FCG, a fund that owns the stocks of companies that derive significant revenue from exploring and producing natural gas. They're listed on the ISE-REVERE Natural Gas Index. Like the Dow, it has 30 components including Apache (APA), Chevron (CVX), Quicksilver Resources (KWK), Noble Energy (NBL), Shell (RDS-A), and Questar (STR). As you can see by the inclusion of Chevron and Shell, it's hardly a natural gas pure play.

Both UNG and USO, targeting the price of natural gas and oil respectively, peaked in July 2008. UNG kept falling all the way to the end of last month, but USO bottomed out in February. From its mid-February price of $23, USO has gained 65%. Since mid-February, UNG has lost 14%, and that's after a 17% pop in the last three weeks. The divergence between the two is obvious.

FCG peaked in June 2008, and bottomed in March. Since its March bottom, it has gained 59%. How much of that is from the excitement over oil and its potential to boost profits at the companies on the index is hard to say, but it's safe to assume a lot.

Many people have written to me about buying UNG, so many that it prompted me to check the popularity of the ETF. In two words: red hot. Its assets under management were only $700 million at the end of March. They hit $2.2 billion at the end of May and surpassed $4.5 billion just last week. More than $2 billion found its way into the fund in the first half of this month alone.