One approach would peg the reserve volume to the time required in an emergency to transition the economy from natural gas to a substitute fuel.

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But wind farms--which substitute for coal as a fuel for electricity--have little to do with oil prices.

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Long term, environmentalists must win their ongoing battle as utilities substitute incremental natural gas as their boiler fuel.

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Ethanol subsidies began decades ago as a small test to see if corn could produce a fuel that would be an appropriate substitute for gasoline.

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