U.S. vehicle sales reached a six-year high in 2013, with 15.6 million units sold, up from 14.5 million in 2012. Demand for some of the top-selling cars was so high that dealers had trouble keeping them in stock.

While sales is an obvious measure of a car’s demand, another industry measure called days supply can also shed light on a model’s popularity. Days supply approximates the amount of time it takes to sell a vehicle from the moment it leaves the manufacturing plant until a customer buys it at a dealership. Car data site TrueCar.com provided 24/7 Wall St. with a list of the models that sold at least 100,000 units through the first 11 months of 2013 and had the lowest days supply in the United States in November. At the top of the list was the Subaru Forester, which had an average days supply of just 26.7 days.

Click here to see the most popular cars in America

One factor that can drive the popularity of a car is a recent redesign. The majority of the cars with the shortest days supply have been redesigned recently. Among these was the Subaru Forester, which launched its latest redesign in 2013 to immense acclaim. The Forester had the lowest average days supply of any car in the U.S. last year. Toyota’s RAV4 (NYSE: TM) was also updated, and the average days supply fell 30.3%. Eric Lyman, vice president of Editorial and Consulting at TrueCar agreed that a brand new look for a model is “definitely is a factor” in reducing the days supply.

Not surprisingly, sales of many of these hot-selling vehicles have increased significantly in the last few years as demand has risen. Sales of the Toyota RAV4 jumped from 171,875 in 2012 to 218,249 in 2013. The Toyota Tacoma, Ford (NYSE: F) Explorer, and Nissan Sentra all clocked in double-digit sales growth as well, while the Forester’s sales soared by more than 60%.

While days supply is indicative of demand, Lyman explained, it is not necessarily the only reason a car model would have low days supply. “The other variable here is incentives. If you lower the price, you can obviously sell more cars. And that doesn’t necessarily mean you have higher demand.” Lyman noted that the Ford Explorer may be the best example of this. In 2012, Ford offered buyers an average discount of $1,972 per unit. In 2013, Ford increased the value of the offered incentives on the vehicle to an average of $3,283. This was more than $300 higher than the segment average incentive for the year.

To determine the eight cars so hot they’re out of stock, 24/7 Wall St. reviewed days supply figures provided by TrueCar, an information and technology platform targeting car buyers. This figure measures the amount of cars in inventory, divided by the daily selling rate, or the number of cars sold in a day. We only used the list of the models that sold at least 100,000 units through the first 11 months of 2013 and had the lowest days supply in the United States in November. Additionally, TrueCar provided figures on annual sales by model and values for incentives offered by dealers. We also reviewed monthly sales reports released by each carmaker.

8. Nissan Sentra
> Average days supply: 46.9 days
> 2013 sales: 129,143
> 1 year change in sales: +21.4%

Spurred by a recent redesign, sales of the Nissan Sentra jumped in 2013. Nissan sold more than 129,000 Sentras in the U.S. last year, with an average of just 47 days supply in November. This marks a major improvement from 2012, when the company sold more than 106,000 cars, each taking an average of 55 days to sell. According to Reuters, Japan-based Nissan sees the Sentra as a key for its growth ambitions in the U.S., with one executive telling the news agency, “we simply can’t build enough Sentras.”

7. Hyundai Sonata
> Average days supply: 42.5 days
> 2013 sales: 203,648
> 1 year change in sales: -11.7%

Despite the fact that the Sonata has a four-cylinder engine, it puts out 190 horsepower, more than rivals Camry, Fusion, and Accord. The three rivals were all among the 20 best-selling models in the U.S. last year. While the Sonata still was one of the hottest-selling cars in 2013, its appeal may have cooled down a bit from the year before. While the company recently announced a redesigned Sonata, Reuters reported some experts consider the design conservative, which could be unappealing to U.S. consumers.

ALSO READ: Top 10 Cars with the Best Resale Value

6. Ford Explorer
> Average days supply: 41.2 days
> 2013 sales: 192,397
> 1 year change in sales: +17.2%

The Explorer is the only Ford-produced top turnover model. Likely, the generous incentive dealers offered Explorer buyers helped boost sales. Explorer dealers offered a $3,283 incentive, $300 more than the average incentive manufacturers gave midsize utility car buyers. The company has struggled with a number of sales-related issues, including slowing sales in Europe, next-to no market presence in Japan, and a long-struggling luxury brand. Still, Ford is the single top-selling car brand in the U.S., and the Explorer is one of its top models.

5. Nissan Versa
> Average days supply: 38.6 days
> 2013 sales: 117,352
> 1 year change in sales: +3.6%

Nissan introduced the Versa sedan in 2007, a year after releasing the Versa hatchback. Named for its proclaimed versatility, the Versa is sold at a suggested price of $11,990, slightly less than the Sentra, Nissan’s other fast-selling model. In addition to updating the Versa sedan for the 2014 model year, Nissan revealed the 2014 Versa Note hatchback at the 2013 North American International Auto Show in Detroit. The Note is a variation on the Versa model, designed and marketed to appeal to millennials, who will soon be among the most sought after consumers as their purchasing power increases.

ALSO READ: America’s Best-Selling Cars

4. Toyota Tacoma
> Average days supply: 38.5 days
> 2013 sales: 159,485
> 1 year change in sales: +12.8%

The Tacoma is so popular that, according to Toyota, as of September, it was “the best-selling compact pickup truck in the U.S. market since 2005.” While Toyota may lead the compact pickup truck market, it is relatively weak in the full-size pickup market. Its offering, the Tundra, is no match for the Ford F-series, Chevrolet Silverado, and Dodge Ram — the three top selling light vehicles in the nation. Additionally, the company issued a recall of 4,000 Tacomas in November, citing defective engine valve springs.

3. Toyota RAV4
> Average days supply: 36.8 days
> 2013 sales: 218,249
> 1 year change in sales: +27.0%

Toyota’s major redesign of the 2013 RAV4 may have contributed to the car’s popularity last year. Sales of the RAV4 jumped by 27% in 2013, compared to an overall 7.6% increase in car and truck sales. As of November last year, the average days supply dropped by 30% to 36.8 days from 52.7 days the year before. In all, the RAV4 was one of the best-selling cars of 2013, with more than 218,000 units sold.

2. Toyota Camry
> Average days supply: 35.6 days
> 2013 sales: 408,484
> 1 year change in sales: +0.9%

In 1983, Toyota redesigned the Corona and introduced it as the Camry in the U.S. The car quickly became one of the country’s top sellers — and this year also one of the hottest. The 2013 model was the best-selling car in the U.S. for the 12th consecutive year, with more than 400,000 units sold last year. Only the Forester sold faster in November last year. However, dealers provided an average of $2,720 in incentives to Camry buyers, or more than $300 more than the incentives offered to other midsize car buyers.

ALSO READ: The Cars Americans Do Not Want to Buy

1. Subaru Forester
> Average days supply: 26.7 days
> 2013 sales: 123,592
> 1 year change in sales: +61.9%

Japan-based Subaru redesigned the Forester for the current model year, introducing the car’s fourth generation. The new version won the prestigious Motor Trend SUV of the year award this year, which likely helped to boost the Forester’s popularity. As of November of last year, the average Forester spent 26.7 days from being shipped to being sold, the least time compared to other top-selling models. Subaru recently reported record annual sales in 2013 in the U.S., Canada and Australia markets. In all three countries, the Forester contributed the most to the strong sales.

Thank you for reading! Have some feedback for us?
Contact the 24/7 Wall St. editorial team.