The cars are especially clean in Norway, where most of the electricity comes from dams, not from burning fossil fuels. But even in countries that burn coal for power, the cars are so efficient they can cut greenhouse-gas emissions by more than half.

The vehicles have one huge problem, though: the battery that makes them possible. The limitations of available battery technology mean that the range of the cars has been limited, typically to less than 100 miles, or 160 kilometers.

But as the market grows, innovation in batteries seems to be taking off. Economies of scale are kicking in. A wave of new cars is coming over the next couple of years, with the manufacturers promising big improvements.

For instance, General Motors is on the verge of shipping the Bolt, a sporty-looking hatchback with a promised range of 238 miles. That is four solid hours of highway driving.

The new cars are expected to cost below $40,000, or 36,000 euros, and in the United States, federal and state tax credits for electric cars will in many places push that below $30,000. Leases are expected to be available at $200 a month, and electricity in most places is far cheaper than an equivalent amount of gasoline.

As of yet, rapid, mass-market adoption should not be considered the likely scenario, according to an October report from Fitch, the financial ratings agency. The oil companies are probably right to expect a long, slow increase for electric cars, the firm found.

But things are moving fast enough that the possibility of a real disruption can no longer be dismissed out of hand.