Unless you're an investor of Volkswagen Group, October turned out to be a pretty solid month for major automakers in the U.S. market. For the entire automotive industry, October's seasonally adjusted annual selling rate hit 18.23 million units, which was the highest mark since July 2005. 

While the dream scenario of cheap financing and low gas prices won't fuel sales of SUVs and trucks forever, Detroit automakers General Motors (NYSE:GM), Ford Motor Company (NYSE:F), and Fiat Chrysler Automobiles (NYSE:FCAU) are all currently major benefactors. Here are some highlights for all three, and what to expect going forward.

GM Headquarters in Detroit. Image source: General Motors.

General Motors
All together, GM's four brands in the U.S. -- Chevrolet, Buick, GMC, and Cadillac -- sold nearly 263,000 vehicles last month, which was a strong 16% gain compared to a year ago. That gain was powered by Chevrolet posting its best October sales volume since 2004, good enough for a 17% gain that generated a whopping 183,000 units of GM's total 262,993.

"The redesign of our full-size trucks and SUVs, and our move into the small crossover and mid-size pickup segments were smart bets, and our timing couldn't be better with industry sales at record levels," said Kurt McNeil, GM's U.S. vice president of Sales Operations, in a press release.

Looking again at GM's key Chevrolet brand, retail sales surged 20% higher, and October marked the seventh consecutive months of year-over-year retail and market share gains. While Chevrolet absolutely turned in a strong month, it's important for investors to note that the year-over-year gains appear slightly inflated due to sales of the Colorado and Trax, which weren't selling at full-speed last October -- the two vehicles combined for over 15,000 units sold this October compared to a meager 1,491 units last year.

Looking at GM's highly profitable full-size trucks, the Chevy Silverado posted a 10% gain in sales last month to more than 51,000 units, and the GMC Sierra recorded a slight decline, but still sold 18,521 units. Also, at a time when incentives have been rising, GM's incentive spending on its full-size pickups declined about $200 per unit, both sequentially and year over year, which should generate a slight boost in profitability.

Ford's Explorer continues to sell well. Image source: Ford Motor Company.

Ford Motor Company
Detroit's second largest automaker checked in with a sales gain of 13% in October, to 213,938 vehicles, which was its best October in 11 years. The story for Ford in October revolved around strong sales of SUVs and its healthy increase in average transaction prices (ATPs).

Looking at SUVs, which remain red hot across the U.S. market, Ford brand SUV sales were up 12% in October, its best October since 2004. That gain was led by the Explorer's 30% sales increase and the Edge's nearly 39% gain, both compared to last year's October. Meanwhile, Ford's bread-and-butter F-Series sales gained only 3.3% over last year's October, but its sales topped 65,000 units, which is an outstanding month.

In part because of the strong demand for Ford's SUVs and full-size trucks, Ford vehicles posted an all-time record for average transaction prices last month -- at $34,600 per vehicle. If you're keeping track, that's a healthy $1,800 higher compared to last year's October, and the largest gain among any major automaker.

Fiat Chrysler Automobiles
FCA reported a 15% increase in sales during October, reaching 195,545 units, which was the automaker's best October month of sales since 2001. All of the brands under FCA in the U.S. market posted year-over-year sales gains led by Jeep's 33% increase in sales during October. Furthermore, eight individual FCA vehicles posted sales records for the month of October.

Jeep remains an extremely hot brand in 2015. Image source: Fiat Chrysler Automobiles.

"October marks our 67th-consecutive month of year-over-year sales growth and our best October since 2001," said Reid Bigland, Head of U.S. Sales, in a press release. "Last month's sales strength continued to be broad based for the company, with eight FCA vehicles setting October sales records across three of our brands."

Zeroing in on FCA's most important products in the U.S. market, those under the Jeep and Ram brand, the results are still good, but not as impressive as they seem at first glance. For instance, though Jeep has consistently delivered strong double-digit growth over the last year and a half, investors need to consider that 7,795 of October's Jeep sales were generated by the Renegade, which has zero units in the previous year's October comparison. That doesn't take away anything from achieving those sales -- after all, that's why you add products to your vehicle lineup -- but it does give a more accurate context for the high 33% increase.

In other news, FCA's full-size Ram pickup truck's sales moved only 3% higher in October to 40,931 units. The Ram trailed Ford's F-Series and General Motors' Silverado's respective gains of 3.3% and 10%, for 65,500 and 51,647 units. Still, all three vehicles are selling at a very high rate in total volume and should generate strong profits for their respective automakers during the fourth quarter. 

Ultimately, October was a strong month for Detroit automakers, and the U.S. auto industry as a whole. Going forward, investors will want to keep an eye on incentive spending as major automakers gear up to take advantage of a strong holiday selling season. Currently, while incentives are rising, they aren't rising as a percentage of average transaction prices. If that stays true throughout the fourth quarter, expect another round of strong earnings reports from major automakers.

Daniel Miller owns shares of Ford and General Motors. The Motley Fool recommends Ford and General Motors. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.