Sales of the two highest-volume plug-in electric cars soared in August, with both the Chevrolet Volt and the Nissan Leaf setting all-time monthly sales records.

And two Toyota plug-ins set sales records as well. The Toyota Prius Plug-In Hybrid sold more than it has all year, and the low-volume RAV4 EV electric crossover utility vehicle, with its Tesla powertrain, set an all-time monthly sales record.

Chevy, in fact, was so confident about the month's Volt sales that GM president Mark Reuss previewed the total last week, telling the Los Angeles Times, "We will do about 3,300 Volt sales this month."

In July, Leaf sales rose but Volt sales fell--so August provided a bright contrast to mixed July figures.

Previous bests

Chevrolet delivered 3,351 Volts in August, totaling just under 15,000 Volts sold for the first two-thirds of 2013. Last month's number is a 24-percent increase over 2013's previous best of 2,698 in June; its sales in July had fallen to 1,788.

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The Volt's previous best-ever sales month was in October 2012, when Chevy sold 2,961--not quite exceeding the 3,000 barrier it broke through this month.

Analysts credit higher incentives and publicity over the $5,000 price reduction on the 2014 Volt for the best-ever number.

The 2,420 Nissan Leaf deliveries in August bring the year's total to 14,123, less than 1,000 units behind the Volt.

The Leaf's previous top sales month was March of this year, when 2,236 were sold, filling several months of pent-up demand after Leaf supply from Japan dried up in advance of volume production from the assembly plant in Smyrna, Tennessee.

“Some of our new wave markets like Atlanta have come on so strong that it makes more sense to count Nissan LEAF days’ supply by the hour," said Erik Gottfried, Nissan's director of electric vehicle sales and marketing.

"Atlanta has about a 120-hour supply" of Leaf electric cars right now, he said.

Best month to date?

If other plug-in cars stay at average levels, August is still likely to register the highest electric-car sales numbers since the Leaf and Volt went on sale in December 2010.

While we had thought the August total might exceed more than 9,000 cars, which would be a new monthly record, in fact it surpassed 10,000 units--about 35 percent up on last month and a new record in the U.S. market.

That means roughly 59,000 plug-in cars have been sold over the first two-thirds of the year.

If the number stays at that level for the final four months, we'll hit an annual rate of more than 100,000 plug-in vehicles sold (out of a total market of perhaps 15 million vehicles this year).

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Neither Fiat nor Tesla Motors [NSDQ:TSLA] sees fit to report monthly sales; Tesla reports on sales in its quarterly financial filings, while Chrysler's parent company simply refuses to break out sales of its low-volume Fiat 500e compliance car from overall 500 sales.

2012 Toyota Prius Plug-In Hybrid, production version road test, San Diego, CA, Jan 2012

2012 Toyota Prius Plug-In Hybrid, production version road test, San Diego, CA, Jan 2012

Plug-in hybrids rise?

The Toyota Prius Plug-In Hybrid had been lagging since the spring, though July's total of 817 was the best since January.

But in August, Toyota more than doubled that number, moving a remarkable 1,791 plug-in Priuses--more than a quarter of the 6,822 total year-to-date.

That's not only its best month this year, but its second-best month ever. Only October 2012 did it exceed that total, with 1,889 sold.

Honda added some Northeast markets to the previously California-only sales of its Accord Plug-In Hybrid, but that car's numbers stayed roughly in line with those of the last two months, at 44 units in August.

With only 298 sold since January, that car's rollout continues to be slow and deliberate.

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In some months, Ford's two plug-in hybrids--the C-Max Energi and Fusion Energi--added together have outsold Toyota's plug-in Prius. That wasn't the case in August, though.

Ford delivered 621 C-Max Energi and 600 Fusion Energi plug-in hybrids, record monthly sales for each model.

It does not seem as if plug-in hybrid sales have been affected by the company's latest backpedaling on C-Max Hybrid gas-mileage ratings and its public dispute with the EPA over those ratings.

2013 Chevrolet Volt

2013 Chevrolet Volt

Low-volume and compliance cars

As well as its record-breaking Volt total, GM delivered 102 Spark EV battery-electric cars--essentially equal to last month's 103--which has now been rolled out to dealers in California and Oregon.

Honda delivered sold 66 of its Fit EV cars in August, on part with July's 63, bringing the year's total thus far to 420 for the lease-only car.

As for the Toyota RAV4 EV, the company managed to deliver 231 of them--its best-ever month, and near double the 133 last March, its previous best month--with a reduced lease price for the all-electric crossover likely to keep sales higher in months to come.

Sales of the Ford Focus Electric were 175, just three shy of the model's all-time best month (in June of this year). Over almost two years, however, less than 2,000 Focus Electrics have found buyers--or less than this month's Nissan Leaf sales alone.

After a flurry of heavily discounted sales at the start of the year, the Mitsubishi i-MiEV appears to have fallen off a cliff. With two thirds of the year gone, Mitsubishi hasn't even sold 1,000 of the electric minicars.

The 30 delivered in August were the lowest total since its first month on sale, back in November 2011, when 4 were delivered. And there's still no word on a 2013 update, as dealers sell through their 2012 models.

The Smart ForTwo Electric Drive is also likely to sell in roughly the same volumes.

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