A growing number of foreign energy companies eager to tap into America's vast natural gas reserves are looking to invest in independent companies, while estimates of US supplies continue to increase.

BP and BG Group of the UK; StatoilHydro, the Norwegian energy company; and Eni, the Italian oil company, have all bought into the US gas industry in the past year to gain access to the US industry while tapping into the independent groups' experience and technical expertise.

PFC Energy, a consultancy, estimates advancements made by the independents – which carry out exploration and production of the natural gas but not refining – in developing natural gas from shale could, if taken abroad, more than quadruple gas resources, increasing supplies of this alternative option to greenhouse-intensive oil, coal and oil sands fuels.