Shares of Tesla (NASDAQ:TSLA) have been on a tear recently. The stock is up 44% in the past six months. While the sharp rise is great for shareholders, it puts the pressure on for the company to execute during its fourth quarter. More specifically, investors should look for continued strong vehicle sales growth from the automaker to confirm that the automaker's growth story is intact.

Fortunately, there are several reasons for investors to be optimistic that Tesla can do exactly this.

A woman unlocks her Model 3 with a Tesla app on her smartphone

Model 3. Image source: Tesla.

Demand is increasing

Demand for Tesla's vehicles has steadily increased throughout the year -- and Q4 was no exception.

"Our global order rate remains strong and continues to increase," said Tesla CFO Zachary Kirkhorn in the company's third-quarter earnings call. "Despite increases to production levels, our order backlog has been growing, and quarter to date, orders are significantly higher than at this point in last quarter."

This bodes well for the company to hit its quarterly and full-year guidance. Tesla said it expected deliveries to increase sequentially and to exceed 360,000 for the full year. This means the electric-car maker will need to deliver over 104,500 vehicles in Q4 -- a figure that implies a 7% sequential increase. That would put total deliveries in 2019 significantly ahead of the 246,000 vehicles it delivered in 2018.

Word-of-mouth marketing is working

As has been the case for Tesla's previous vehicles, word-of-mouth marketing for Model 3 is proving effective.

"[W]hat we're seeing is that word of mouth is more than enough to drive our demand in excess of production. We have no plans to advertise at this time," Tesla CEO Elon Musk said.

Of course, Tesla does engage in significant sales efforts by opening stores in high foot-traffic areas, hosting occasional test-drive events, implementing referral programs, and utilizing other marketing tactics. Still, it's good to see Tesla reporting that word-of-mouth marketing remains a meaningful sales driver.

Model S and X deliveries may rebound in Q4

While Model 3 deliveries have been rising sharply, sales of Tesla's higher-priced Model S and X have been concerning. After averaging about 25,000 combined Model S and X deliveries a quarter throughout both 2017 and 2018, sales of the two vehicles have been dropped significantly in 2019. In Tesla's third quarter, for instance, combined Model S and X deliveries were about 17,500, down 37% year over year and 1% sequentially.

But Tesla management surprisingly indicated that deliveries of the two vehicles could move higher during Q4.

"[W]e are increasing production on our S and X lines for this quarter in response to increasing demand," said Kirkhorn during the call. He noted that while the Model 3's production ramp has consumed attention at the company up until this point, the recent stabilization of Model 3 production is allowing Tesla to focus more on the balance between its three vehicles. "So, the delivery numbers in Q3 understated the interest in the product for that quarter," he explained. "And we continue to see strength in the order rate, which we anticipate will be reflected in S and X deliveries in Q4."

Given all these comments from management on recent demand trends, record total vehicle deliveries in Q4 seem likely.