This might be a good time to invest in the natural-gas industry, given that the commodity is extremely cheap.

If you live in or near Pennsylvania, you have heard of the Marcellus Shale natural-gas discovery, which some have considered to be the Saudi Arabia of natural gas.

That boom is highlighting how money can be made in this source of energy. But trading in natural gas itself isn't the way to go; commodity markets are highly volatile and can swing wildly in price, as much as 50 percent in a few days.

The underlying price of natural gas as a commodity is near historic lows. The price hovers around an abysmal $3 per thousand cubic feet (Mcf), down from a peak of $13.28 on July 1, 2008 (Henry Hub Natural Gas spot price).

So investment advisers and portfolio managers are looking at backdoor ways to profit from the shale-gas boom. There is the switch by utilities to natural gas from coal. There are companies helping to build out what Goldman Sachs has dubbed the "shale gas revolution." There are now engine builders keyed to natural gas.

"You have to find the companies that benefit from the switch on the cost side," says JPMorgan investment specialist Chris Millard, based in Philadelphia.

The fundamental case for investing in natural gas, according to Goldman, is not a good one if you solely consider the current price. A boom in production of late has led to a temporary but money-losing oversupply, but there is the prospect of a more balanced market next year and beyond. Though there is a glut of natural gas in this country, even with utilities cranking because of the heat wave, Goldman sees an upside to prices in 2013, saying natural gas could rise to $4 in the next year.

Goldman recommends companies building out the infrastructure for natural gas, which many see as the country's savior from higher-priced imported oil.

Among Goldman's recommendations are KBR (symbol: KBR), the global engineering and construction company, for which Sachs holds a 12-month price target of $47 a share, up from $23 currently, and Chicago Bridge and Iron (CBI), with a $55 12-month price target, up from $37 currently.

"They are among the key leaders ... in the multiyear investment cycle to build out the shale gas revolution, where we estimate at least $60 billion in incremental spend," the firm noted.

Both KBR and Chicago Bridge and Iron are involved in gas processing, which makes the wellhead gas suitable for downstream use; fractionation, which separates the various natural gas liquids; ethylene development, and the export of low-cost North American liquid natural gas to other countries for a much higher price.

Goldman also recommends Babcock & Wilcox Company (BWC) with a $32, 12-month price target. A power infrastructure company, Babcock & Wilcox should benefit from the Environmental Protection Agency's enforcement of the so-called CSAPR and MATS regulations, acronyms for the Cross-State Air Pollution Rule and Mercury and Air Toxics Standards.

Bryn Mawr Trust, on the other hand, leans toward oil producers with some natural-gas exposure, which in the long-term are plays that should benefit from the switchover from coal and oil by American industry.

EOG Resources (EOG), the largest leaseholder in Texas' Eagle Ford shale formation, is a favorite for Bryn Mawr Trust client portfolios. EOG's share price tends to rise and fall with the price of oil, leveraged about 70 percent to the oil price and 30 percent to natural gas.

"We know they have conservative accounting, quality management, and they are a low-cost producer," unlike the troubled Chesapeake Energy (CHK), says Bryn Mawr chief investment officer Ernest Cecilia. He analyzed Chesapeake years ago and didn't like it - even before the recent revelation that its CEO borrowed a large amount of money, using company assets, to further his own financial standing, and did not disclose it.

The firm definitively does not recommend exchange-traded funds in natural gas: "We shy away from ETFs for those individuals looking for exposure in natural gas. We don't traffic in it," says Cecilia. The United States Natural Gas Fund (UNG) is a good illustration for not trading in natural gas contracts or funds that hold them - the fund has a high correlation with the underlying natural gas price, which has been sinking.

Cummins Inc. (CMI), which manufactures and services fuel-related technologies, is exposed to engine and power-generation demand and is well-positioned to benefit from European engine regulations and China's engine standards. Cummins may increase its dividend, with management continuing to return 35 percent of operating-cash flow to shareholders, says Joe Costigan, who runs small/mid-cap and large-cap portfolios for Bryn Mawr Trust. He thinks Cummins is worth at least $125 a share, up from where it trades at $95 currently.

"It has a nice secular trend behind it, and we've been buying it for clients since the end of 2011," said Costigan.