We've got used to seeing plug-in car sales inexorably rising over the last few years.

Different models sell at different rates of course, but when one or two cars each month hit some kind of individual sales record, the growth is rarely remarkable.

But every so often we're taken by surprise by one car's performance. This month, it's that of the 2014 Ford Fusion Energi plug-in hybrid--which, for the first time ever, has out-sold the Chevrolet Volt.

It's true: Not only did the Fusion Energi see off the Toyota Prius Plug-In Hybrid this month, but at 1,939 deliveries it also beat the consistent-selling Chevrolet Volt, on 1,777 units.

In fact, it was the Fusion Energi's best-ever month on sale, beating its previous best--one month earlier--by nearly 600 units.

In technical specification, there isn't much similarity between the Volt, on sale since 2010, and its more recent rival.

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Where the Volt uses a primarily plug-in drivetrain, with a 38-mile all-electric range and 1.4-liter engine serving as a "range extender", the Fusion uses a more conventional 2.0-liter four-cylinder as its primary powerplant and supplements it with an electric motor.

On paper though, each is quite similar.

There's less than $600 between the two cars on price, at least at the entry-level--the Volt's $34,995 sticker price just a shade below the Fusion Energi's $35,525.

2014 Chevrolet Volt

2014 Chevrolet Volt

Each also returns similar gas mileage when its battery isn't being utilized: the 2014 Volt is rated at 37 mpg combined by the EPA, the Fusion at 38 mpg combined.

The Volt fights back with its 38-mile electric range though, something the 20-mile blended electric range of the Energi can't match. In return, the four-seat Chevy Volt isn't as practical as the five-seat Fusion.

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So what could be behind the Fusion's sales spurt?

It's perhaps too early to tell--and June's sales may not reflect that the Fusion Energi was recently shorn of a few MPG by the EPA.

The Fusion's sales have certainly risen for the past few months, but in general its monthly tallies have lacked the consistency of the Volt.

On the other hand, with rumors circulating of the next-gen Volt, we may see Volt sales slow as customers wait for a newer model--it's likely the Ford could start to beat the Volt more regularly.

The real winner though is the industry. June was the second-best ever month for plug-in car sales in the U.S.--and whichever model tops the sales charts over the coming months, it's clear that plug-in vehicles are only going to get more popular.


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