Crude-oil costs are a bigger slice of the prices American consumers pay for petrol: lower sales taxes and fuel duties mean swings in oil markets have a bigger effect on pump prices.

ECONOMIST: Debt and deflation

But the Asian producers started making more SUVs and pickup trucks in their North American factories to escape the duties, and then a rising oil-price led many motorists to abandon these often gas-guzzling vehicles.

ECONOMIST: Ford

Fuels would be taxed according to their CO2-generating potential (ie, coal more than oil, and oil more than gas) rather than the miscellaneous system of duties to which they are now subjected.

ECONOMIST: A cooling off period

In most of the Gulf states, which do not even levy income tax, duties are the third-biggest source of government finance after oil exports and investment income.

ECONOMIST: Middle Eastern smugglers

But this still commits the party to raising fuel duties year by year in line with inflation, no matter how high the world oil price rises.

ECONOMIST: British election briefing: Transport

The government's plan to curb car use by raising fuel duties by at least 5% in real terms annually has been undermined by weak oil prices.

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