Walmart (NYSE:WMT) impressed investors on Tuesday with solid financial results for its fourth quarter of fiscal 2019. Revenue rose 3.1% year over year when excluding currency changes. In addition, the company's comparable-store sales increased 4.2% year over year in the U.S. -- an acceleration from 3.4% growth in Q3. Walmart also announced a 2% dividend increase, marking the company's 46th year in a row of increasing its quarterly dividend. 

But one of the most optimistic takeaways from Walmart's fourth-quarter update may be its lasting strong momentum in e-commerce. The company's success in e-commerce will ultimately determine how well it can thwart rising competition from Amazon.com (NASDAQ:AMZN) and brick-and-mortar peers, such as Costco (NASDAQ:COST), which are similarly vying to sell more goods online.

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Walmart's fast-growing online sales

In Walmart's fourth quarter, which includes the important holiday season, U.S. e-commerce sales soared 43% year over year. Notably, Walmart had posted the same strong year-over-year growth rate in U.S. e-commerce sales in the previous quarter.

Strong e-commerce sales for Walmart in Q4 put the full-year figure for the segment up 40% year over year.

It's good to see Walmart's U.S. e-commerce sales growing at such a steep rate, especially since investors watched the retailer's e-commerce sales in the key market rapidly decelerate this time last year. U.S. e-commerce sales reached 50% year-over-year growth in the third quarter of fiscal 2018 but slowed to 23% in the fourth quarter of fiscal 2018 and came in at 33% in the first quarter of fiscal 2019. Investors were worried that sales growth for the segment would remain at these lower levels.

But Walmart's year-over-year U.S. e-commerce sales growth picked up as fiscal 2019 went on, growing 40% in Q2, 43% in Q3, and 43% again in Q4.

"Walmart U.S. eCommerce continued to benefit from the expansion of grocery pickup and delivery and a broader assortment on Walmart.com," the company said in its fourth-quarter earnings release on Tuesday.

Notably, e-commerce sales from Walmart's Sam's Club wholesale stores rose 21% year over year in Q4.

Check out the latest Walmart earnings call transcript.

How does this compare to peers?

Walmart's momentum in e-commerce sales stacks up nicely against what peers are seeing. Target's (NYSE:TGT) comparable e-commerce sales for its November and December period were up 29% year over year. While not a perfect comparison with Walmart's full fourth quarter, it suggests Walmart is seeing greater growth in its online sales than Target. In this regard, Walmart has higher expectations for the full year, guiding for U.S. e-commerce sales to increase about 35% this year compared to last year; for reference, Target expects digital sales to rise more than 25% in 2019.

Meanwhile, Costco's e-commerce sales for the 18 weeks ended Jan. 6 increased about 28% year over year (slower than Walmart but faster than Sam's Club), and Amazon's revenue from online stores increased 14% year over year in its fourth quarter.

In a nutshell, Walmart is holding up well in e-commerce. And guidance for more strong growth in online sales in fiscal 2020 points to management's optimism that this momentum can continue.