Shale gas is an unconventional natural gas produced from shale, a type of sedimentary rock. Shale gas has become an increasingly important source of natural gas in the United States over the past decade, and interest has spread to potential gas shales in Canada, Europe, Asia, and Australia. One analyst expects shale gas to supply as much as half the natural gas production in North America by 2020. In a 2013 report, the US Energy Information Administration estimated the quantity of technically recoverable shale gas for 41 countries. North America leads the worldwide production of shale gas, with the US and Canada having significant levels. Beyond the US and Canada, shale gas is so far produced at a commercial scale only in Argentina and China. While the shale gas potential of many nations seems promising, there are several obstacles spanning several economic, environmental, technical and social issues grouped in major categories such as access to resources, infrastructure and governance. Shale gas production has been blocked in many countries largely because of the environmental risks involved. These risks and social concerns have resulted in legal restrictions on hydraulic fracturing, that have prevented a more extensive development of shale gas worldwide. Africa South Africa South Africa has a major sedimentary basin that contains thick organic-rich shales: the Karoo Basin in central and southern South Africa. The Karoo Basin is large, extending across nearly two-thirds of the country, with the southern portion of the basin potentially favorable for shale gas. However, the basin contains significant areas of igneous sill intrusions that may impact the quality of the shale gas resources, limit the use of seismic imaging, and increase the risks of shale gas exploration. The Karoo is estimated to have technically recoverable resource of 485 trillion cubic feet (Tcf) of gas. Several companies intend to explore for shale gas using hydraulic fracturing in the Karoo region. This is bitterly opposed by a coalition of environmentalists, farmers and local residents. Falcon Oil & Gas Ltd. was an early entrant into the shale gas play of South Africa, obtaining an 11,600-mi2 (30,000-km2) Technical Cooperation Permit (TCP) along the southern edge of the Karoo Basin. Shell obtained a larger 71,400-mi2 (185,000-km2) TCP surrounding the Falcon area, while Sunset Energy holds a 1,780 mi2 (4,600-km2) TCP to the west of Falcon. The Sasol/Chesapeake/Statoil JV TCP area of 34,000-mi2 (88,000-km2) and the Anglo Coal TCP application area of