Just as diesel fuel isn't available at every single gas station, diesel vehicles are unevenly distributed in the United States.

And despite double-digit rises in registration numbers, the preponderance of diesel engines in North America remain in trucks--especially heavy-duty trucks--rather than passenger cars.

DON'T MISS: Fewer Gas Stations, But More Diesel Pumps, As Diesel Sales Rise

Data provided by IHS Automotive to the Diesel Technology Forum indicates that sales of diesel cars and SUVs rose 13.5 percent last year over 2013.

That compares to an increase in overall U.S. vehicle sales of 5.8 percent, according to data from the Alliance of Automobile Manufacturers.

The data showed that the highest increases in diesel registrations came in California, Massachusetts and Nevada, with year-over-year increases of 23.7 percent, 21.0 percent, and 17.8 percent respectively.

'Diesel fuel only' caution on Audi Q7 TDI

'Diesel fuel only' caution on Audi Q7 TDI

In its press release, the Forum also helpfully noted that California is alone among U.S. states in having more hybrids on the road than diesel vehicles.

Western states, including Idaho, Montana, and Nevada have the highest percentage of diesel vehicles on their roads.

There are now a total of 7.4 million diesel cars and SUVs on U.S. roads, out of a total vehicle pool of roughly 250 million.

ALSO SEE: Diesel Engines Selling Well In Large Luxury SUVs & Crossovers

That's an increase of 47.6 percent since 2010, compared to an overall market rise of just 6.4 percent during the same period.

However, in digging more deeply into the data, it turns out that those diesel registrations are not evenly distributed among vehicle types.

Top 10 Diesel States In U.S. For 2014 [Diesel Technology Forum using data from IHS Automotive]

Top 10 Diesel States In U.S. For 2014 [Diesel Technology Forum using data from IHS Automotive]

The Diesel Technology Forum notes that sales of diesel passenger cars and SUVs rose, but the total registration data aggregated for the group includes passenger cars, SUVs, vans, and so-called light-duty pickup trucks.

Presently, the Ram 1500 full-size pickup is the only such light-duty truck offered with a diesel option.

But, according to the Forum's Steve Hansen, those numbers also include "heavy-duty diesel-powered pickup trucks specified for up to 14,000 pounds of gross vehicle weight."

Those are heavy-duty (or "Super Duty") pickups like the Ford F-250 and F-350 lines, vehicles used almost entirely by businesses rather than for daily personal transportation.

Regrettably, the links to additional supporting data charts in the press release we received 11 days ago are now apparently defunct.

And the Forum's website now points to an article on the Hydrocarbon Engineering site that covers the study.

MORE: Diesel To Remain Dominant For Decades In Trucking?

So we don't presently know exactly what percentages of overall U.S. diesel vehicles on the road are what we might consider non-passenger vehicles: the heaviest pickup trucks and vans.

We'll follow up as we get more information.


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