The long-term outlook on natural gas is extremely bright, given the commodity's low prices and attractive qualities, and the time to invest is now, prominent money managers say.

Jeffery Gundlach, whose DoubleLine Capital firm manages about $28 billion in assets, recommended gas investments, such as master limited partnerships, for a 10- to 20-year horizon.

Gundlach said gas, like his gold investment from the early 2000s, could eventually quintuple in price, according to Joshua Brown, a financial blogger and investment adviser.

Jeremy Grantham, whose firm GMO LLC oversees nearly $100 billion, wrote recently in a newsletter that everyone who has a brain should be thinking of how to make money on gas in the long term.

At the end of 2011, three of the 15 most-overweight stocks in the Standard & Poor's 500 index by hedge funds were natural gas-related, Institutional Investor reported.

In recent years, however, natural gas prices have fallen sharply, from a 2008 high of over $15 per 1 million British thermal units, or BTU, to as low as $2.18 per 1 million BTU this year.

Experts don't think natural gas prices will recover anytime soon. In an interview with Bloomberg News, Hsulin Peng, an analyst with Robert W. Baird & Co., expects prices to average between $2 and $3 per 1 million BTU and rise to only $5 per 1 million BTU in 2015.

The main reasons for this bearishness, and why gas prices plunged in the first place, is the quicker-than-expected advancement in hydraulic fracturing, or fracking, the technology that enables gas trapped in underground rock to be extracted by blasting a mixture of water, chemicals and sand. This has enabled drillers to tap previously inaccessible sources and develop an abundant supply of gas, thereby driving down prices.

This winter's mild winter reduces demand for gas as a heating fuel also helped push down prices.

However, at just a hair above $2 per 1 million BTU, natural gas is dirt-cheap by historic standards when compared with crude oil.

Grantham, whose GMO produced the chart below, believes such an extreme historic anomaly -- gas is about 14 percent of the price of its crude-oil energy equivalent, the lowest ratio in almost 50 years -- will eventually revert back to the mean.

Natural gas is, for most purposes like home heating and electric utility plants, a better and cleaner fuel than oil or coal, he said regarding the fuel's long-term future.

The International Energy Agency, or IEA, cites low greenhouse-gas emissions, availability (thanks to improving fracking technology) and geographic diversity (which allay energy security concerns) among advantages of natural gas.

The United Nations-affiliated IEA thinks global gas demand could increase by about 65 percent by 2035 from 2008 levels.

The dominant use of natural gas will still be power generation, but increasing demand will come from the manufacturing, transportation and building industries, the IEA said.