Reserves of shale gas are enormous on all continents, but few basins offer such favorable recovery conditions and such low production costs as do the best half-dozen basins in the United States. Most important, many gas-rich basins have no ready access to the large volumes of water needed for fracking. This is particularly true in China, the country that has perhaps the world’s largest shale gas resources and which would benefit most from their development.
             —-  Vaclav Smil, It’s Too Soon To Judge Shale Gas, IEEE Spectrum February 2015