Miners and their canaries are used to thinking of natural gas as a potentially deadly impediment to digging up coal. It is present in many seams, and poses a danger to humans and birds alike. But gas is becoming increasingly scarce, while coal remains abundant, so many firms are reversing the normal pattern and harvesting the gas, but ignoring the coal. This business, known as coal-bed methane or coal-seam gas, first took off in America, but has now spread. On June 24th, in a sign that the industry had come of age, bg, a British energy firm (which shares a chairman with The Economist), offered to buy Origin Energy, Australia's largest coal-bed methane firm, for A$13.8 billion ($13.2 billion).
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