NEW YORK ( TheStreet) -- More big energy companies have been investing in shale gas fields in the U.S., and this trend is likely to continue.Recent forays by Indian Billionaire Mukesh Ambani's Reliance Industries and by U.K.-based BG Group (through a joint venture with EXCO Resources ( XCO)) into shale in the southern U.S. speak volumes about the growth potential in this space. Shale gas has solved the problem of excessive U.S. and European dependence on imported natural gas. It is now believed that the U.S. can satisfy its natural-gas hunger for at least another 100 years, if not more. Technological advancements along with the process of hydraulic fracturing (also known as fracking) have helped companies gain access to shale gas that was once considered beyond their reach. Russian energy major Gazprom is reportedly mulling a foray into the U.S. shale gas market due to the company's declining market share coupled with falling European demand. Another Asian economy that is looking to meet its insatiable natural gas demand is China. Although the International Energy Agency estimates shale gas reserves of 26 trillion cubic meters in China, the country has not been able to tap these reserves due to lack of drilling know-how. In order to combat this problem, China's largest listed gas producer, PetroChina ( PTR), and Royal Dutch Shell ( RDS.A) partnered to develop shale gas resources in China's Sichuan province. PetroChina has also planned $60 billion in overseas investments to boost its oil and gas output, following peers like China Petroleum & Chemical Corp ( SNP) and Cnooc ( CEO). Shale gas fields in the U.S. such as Marcellus, Haynesville, Barnett and Eagle Ford seem like potential purchase or joint-venture targets by these Chinese companies, or for that matter, European majors like BP ( BP) and Shell. With more companies around the world scouting for shale gas, valuations in shale gas fields have seen a surge. Reliance paid $1.315 billion, $11,144 per acre, to acquire a 45% stake (118,000 acres) in the Eagle Ford shale field owned by Pioneer Natural Resources ( PXD). Earlier in March, BP acquired 80,000 acres in the same region for $200 million, or $4,000 per acre. Shares of companies that operate in Marcellus and Haynesville shale gas fields have lost anywhere between 5% and 50% during the last three months. Major losers include Anadarko Petroleum ( APC), Carrizo Oil & Gas ( CRZO) and Goodrich Petroleum ( GDP). Mid-size companies such as Unit Corp ( UNT), Forest Oil ( FST), and Questar ( STR) are among the few gainers that are still trading at attractive valuations.