As a measure of how dominant pickups have become for American car companies, Ford Motor Co.’s (NYSE: F) F-Series, the best-selling vehicle in the United States, is now 27% of the manufacturer’s sales. And sales of the F-Series are growing faster than the total sales of Ford.

Over the course of the first five months of 2014, Ford sold 305,265 F-Series pickups, a gain of 1.9% compared to the same period a year ago. Ford’s total sales during that time dropped 1% to 1,043,961. The F-Series is not alone at the top of the best-selling vehicle list. The second vehicle among the top 20 is General Motors Co.’s (NYSE: GM) Chevy Silverado, which sold 197,160 units in the first five months, followed Chrysler‘s Dodge Ram, which had sales of 170,711.

Ford’s flagship is not without challenges. Ram sales have shot up 21.4% this year. Among the top 20 selling vehicles in the United States through May, its growth rate is second to only that of the Nissan Sentra, with an increase of 36.6%. Ram sales could pass those of Silverado this year.

While the increase rate of F-Series sales may not match that of the Ram, Ford has the huge advantage that there are only three pickups in the market. Most sedans, coupes and SUVs compete in segments with vehicles built and marketed by manufacturers from Europe, Japan and Korea. None of these companies has been able to crack the full-sized pickup market, despite considerable effort. A large segment with only three competitors is unprecedented.

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Aside from a brand that has been in the market for decades, and which has been the top-selling vehicle in the United States for most of that period, the F-Series has several advantages. The most important of these is the range of models. The F-150 has a base price of $25,025. Model prices rise as high as $50,985 for the top-end Limited model. With accessories, the price of the Limited can rise to nearly $55,000. Ford also builds larger pickups as part of the F-Series line. The biggest of these is the F-450 Super Duty, with a price that rises to $68,790 for the Platinum division.

Under high-praised CEO Alan Mulally, Ford introduced dozens of cars and trucks. One of the marks of the F-Series is that none of those ever came close to its position as the company’s best-selling vehicle.

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