General Motors (NYSE:GM) had another terrific month for U.S. sales in September. GM said its U.S. sales rose 12% last month versus the year-ago period, on strong pickup truck sales and big gains for its revamped lineup of crossover SUVs. 

That was well ahead of rival Ford Motor Company's (NYSE:F) 8.7% increase, and it also beat analysts' expectations. Wall Street analysts polled by Bloomberg had called for a 7.9% year-over-year sales gain for GM, on average. 

In addition, GM's sales gain likely outpaced the overall U.S. market's gain, meaning GM probably gained market share in September.

A wine-red 2018 Chevrolet Traverse crossover SUV parked with mountains in the background.

The all-new 2018 Chevrolet Traverse is now arriving at U.S. dealers. Sales have been very brisk. Image source: General Motors.

By the numbers: GM's new crossovers are winning lots of new buyers

Over the last year, GM has launched all-new and much-improved versions of nearly all of its so-called "crossover" models. The vehicles had been in the works for a few years, but GM's timing turned out to be great: U.S. demand for crossovers has soared, and GM's new models have arrived with good reviews in a hot market.

(Crossovers, sometimes referred to as "crossover SUVs," are so named because they "cross" the size and capabilities of SUVs with the architecture and driving characteristics of sedans. Generally speaking, crossovers are more fuel efficient and smoother-riding than the truck-based SUVs of old, while offering similar interior space and, often, comparable bad-weather handling.) 

Here's how all of GM's crossovers performed in September. Note that most are all-new to the U.S. market since the beginning of 2016. 

Model September 2017 Sales Change vs. September 2016
Buick Enclave (new for 2018; see note) 3,991 0.5%
Buick Encore (refreshed for 2017) 8,262 13.2% 
Buick Envision (new for 2017) 2,300 39.6% 
Cadillac XT5 (new for 2017) 7,302 58.5% 
Chevrolet Equinox (new for 2018) 27,512 80.3% 
Chevrolet Traverse (new for 2018; see note) 11,943 50.8% 
Chevrolet Trax 8,423 (1.2%) 
GMC Acadia (new for 2017) 7,564 11.3% 
GMC Terrain (new for 2018) 9,116 61.2% 

DATA SOURCE: GENERAL MOTORS. VEHICLES MARKED "NEW" ARE MODELS THAT HAVE BEEN INTRODUCED TO THE U.S. MARKET AS "ALL-NEW" SINCE THE BEGINNING OF 2016. THE BUICK ENVISION WAS FIRST LAUNCHED IN THE CHINESE MARKET IN 2014, BUT IT'S INCLUDED IN THE "NEW" GROUP AS IT MADE ITS U.S. DEBUT IN EARLY 2016. ALL-NEW VERSIONS OF THE BUICK ENCLAVE AND CHEVROLET TRAVERSE ARE JUST NOW ARRIVING AT DEALERS; SALES REFLECT A MIX OF OLD AND NEW MODELS. 

As was true in August, demand for GM's new crossovers was again very strong in September. This is significant for GM investors: GM executives have acknowledged that the U.S. new-car market is likely past its peak, but they have been betting that strong demand for (and strong pricing of) the new crossovers would help offset any profit impact from the weakening market. 

Trucks also helped, but sedans remain a weak point

GM's full-size pickups also had a good month, helped by strong demand from commercial- and government-fleet buyers. Sales of the Chevrolet Silverado and GMC Sierra were up a combined 15.6% from September of 2016, reflecting a strong overall truck market. (The rival Ford F-Series posted a 21.4% sales gain in September, helped by strong commercial-fleet demand for Ford's new Super Duty models.) 

A black 2017 GMC Sierra Denali HD pickup, in a parking lot surrounded by trees.

Sales of GM's full-size pickups have been good in a strong market. Heavily optioned "high-series" models like GMC's Sierra Denali HD have helped boost profit margins. Image source: General Motors.

Between trucks and crossovers, the Chevrolet and GMC brands both posted solid overall sales gains for the month, up 17.4% and 9.4%, respectively.

GM's car models didn't fare as well, reflecting larger trends across the industry. All of GM's Buick and Cadillac-brand car models were down year over year by double-digit percentages. The Chevrolet Cruze, Malibu, and Impala all managed modest gains, though. Bright spots: Chevy Camaro sales rose 13%, and the electric Chevrolet Bolt EV had its best month yet, with 2,632 sold. 

The story here is simple and (for GM) not a bad one in context: More buyers are choosing crossovers instead of sedans. For GM, with a fresh and popular line of crossovers that are likely more profitable than comparable sedan models, that's good news. But it has been a tough ride in particular for GM's Cadillac brand, which has well-regarded sedans -- but only one crossover model at the moment. (Several more new Cadillac crossovers are expected over the next couple of years.) 

A black 2017 Chevrolet Bolt EV hatchback parked near a mountain road in bright sunlight.

The battery-electric Chevrolet Bolt EV had its best sales month yet in September, with 2,632 sold. Image source: General Motors.

GM's incentive spending was high in September

GM said its incentive spending, expressed as a percentage of average transaction prices, was 14.6% in September. That's a high number, but GM noted that it reflected the effects of disaster-relief programs that it offered in the wake of the hurricanes that hit Texas, Florida, Puerto Rico, and the U.S. Virgin Islands. TrueCar estimated that GM spent an average of $4,919 per vehicle on incentives in September, up 6.3% from a year ago and more than any other major automaker. 

The upshot for investors: GM probably had a very profitable quarter 

GM's incentives were high in September. That's something to watch, but in GM's defense, its incentives year to date have been well in line with competitors', for the most part. 

More broadly, GM is posting very good sales gains for some of its most profitable products. A few of its new crossovers (the Chevrolet Equinox and Cadillac XT5 among them) appear to be bona-fide hits, a very good situation for GM's bottom line. 

Between the crossovers' success and strong ongoing sales of GM's full-size pickups, it looks likely that GM booked a nice profit in North America in the third quarter. We'll find out for sure when GM reports its third-quarter earnings on October 24.

John Rosevear owns shares of Ford and General Motors. The Motley Fool owns shares of and recommends Ford. The Motley Fool recommends TrueCar. The Motley Fool has a disclosure policy.