Southwestern Energy produces mostly natural gas in the US. It also has net tangible assets (including proven reserves) of roughly $4bn (approx. $12bn assets and $8bn debt). Investment entry price was around $5bn market cap.
This business values cheaply on classic valuation metrics, when purchased the price/earnings ratio was about 1, and the price/book ratio was near there as well. The risks here are the natural gas prices and the ability of the company to maintain cash flow to cover the large debt with increasing interest rates.
Though the net tangible assets appear to present a margin of safety, the value of the assets themselves will fluctuate with the energy market, and there is no guarantee that management will maintain the net asset value going forward (the opposite may be possible given the large cash flow and relatively low profit, and their interests in acquisition).
Some books relating to SWN and its industry are:The Prize: The Epic Quest for Oil, Money, and Power by Daniel Yergin - Pulitzer Prize-winning book about the energy sector as a whole.
The Frackers: The Outrageous Inside Story of the New Billionaire Wildcatters by Gregory Zuckerman – Looks into the growth of independent shale oil and gas producers in the US.