At the BMW auto factory in Leipzig, Germany, workers in dark blue overalls are busy putting together i3 compact electric cars and i8 plug-in hybrid sports coupes, as the plant ramps up production to meet greater global demand.

"We do think the curve is going up," said Michael Blabst, plant spokesman, speaking to reporters attending the International Transport Forum last month. He said that by 2025, 10 percent to 25 percent of BMW's production will be electric and hybrid.

Emission regulations, gas prices, and concerns about climate change are driving the appeal of electric cars worldwide. The biggest market now is China, but electrics are also slowly gaining in popularity in the United States, particularly California, where the mild climate and pro-green regulations favor electrics, market observers say.

Challenges for electric car sales in the United States include their relatively high price, range limits, the varied availability of charging stations, and extreme weather, which can cut into a battery's charge, market observers say.

But the rising price of gas may help increase demand for electrics in the United States this year, said John Voelcker, former editor of Green Car Reports. He said that a small, gradual increase in gas prices, like a quarter a year, would make little difference, but bigger jumps like the kind seen in recent months can change behavior.

"When it spikes, people get scared," Voelcker said.

Gina Coplon-Newfield, director of the Clean Transportation for All Campaign at the Sierra Club, said a gas price spike may encourage people already considering an electric to say "now's the time."

Even more important for consumers than the price of gas is the price of cars, said Voelcker, who sees wider adoption of electric vehicles happening when prices fall enough to be comparable or close to gasoline vehicles of the same size, if the car has 200 miles or more of range.

With the help of tax credits, this is starting to happen. A Nissan Leaf in 2011 had a range of just 74 miles on a charge and cost $35,000, while a similar hatchback cost $17,000 to $20,000, Voelcker said. Now the Leaf has 151 miles of range and starts around $30,000, dropping to $22,500 with a $7,500 federal tax credit.

Except among ardent environmentalists, price is a bigger motivator to buy electric vehicles than the fact that they give off zero emissions, Voelcker said.

"It makes it a more thinkable purchase," he said. "As more of these get out there, people will get more familiar with them. A lot of Americans don't know they exist. As more people see it, they see it's a real car, it's got a stereo, it goes highway speeds. It's going to be a slow build."

Powered by a rechargeable battery instead of gas, electric vehicles still make up a tiny part of cars purchased in the United States. About 18,000 electrics were sold in the U.S. in 2011, and the number was close to 200,000 last year, with over a million globally, Voelcker said.

That represents a small fraction of the 17.2 million U.S. new vehicles sold last year, said Michelle Krebs, executive analyst for Autotrader. She said the limited variety of vehicles available is a handicap.

"People want sport-utility vehicles, and they're willing to pay the gas prices," said Krebs, who believes there is not much consumer appetite for electrics in the U.S. She said electric car companies need to extend range and offer more vehicle types besides sedans.

Manufacturers of higher-cost electric vehicles include Tesla and BMW, while lower-priced options include the Volkswagen e-Golf, the Leaf, and the Chevy Bolt. Tesla also is trying to compete in the lower-cost market with its Model 3, though it has had production problems.

I got to drive a 2018 Nissan Leaf around suburban Naperville, Ill., last month during the Clean Drives Conference, hosted by Midwest Clean Cities coalitions. I found it eerily quiet, with nice pickup.

One interesting feature was the e-Pedal, which allows you to accelerate, slow down, and stop while using just one pedal, instead of both a "gas" pedal and the brake. It felt counterintuitive, but you get used to it. There is also an autonomous driving feature called Pro-Pilot Assist that will search out highway lane markings and help you steer, though you must keep your hands on the wheel.

"I think most people don't realize how nice these cars are to drive," said Coplon-Newfield, who owns a Leaf and a plug-in Toyota Prius.

Cynthia Maves, electric vehicle fleet business development manager for Nissan, said electric vehicle buyers include techies and people with long commutes who want to save money on gas.

But drivers need a way to charge their cars nearby or an electric may not be practical. The number of public charging stations is growing gradually, according to the electric vehicle charging network ChargePoint, which is among a number of websites that include a "find a station" feature.