Istockanalyst.com reported that Coal, Natural Gas - The Best Energy Investment You Can Make This Year:

The coal-to-gas ratio measures the price of each fuel per MMBTU. So when the ratio is 1, the amount of coal needed to generate one MMBTU costs the same as the amount of natural gas needed to generate one MMBTU. When the ratio is below 1, burning gas costs more than burning coal. When the ratio exceeds 1, coal is more expensive.

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