(AMZN -0.18%) stock was the subject of rosy commentary by two analysts this week. Both analysts believe shares have meaningful upside in 2019, citing the company's fast-growing cloud-computing and advertising businesses as key catalysts.

Though e-commerce accounts for the bulk of Amazon's sales, the consumer-facing business has a smaller influence on the company's profits. Amazon's cloud-computing business, Amazon Web Services (AWS), is the key driver for the company's profits -- and Amazon's fast-growing advertising business is quickly morphing into a lucrative contributor, too. This is why two analysts with a buy rating on Amazon stock are citing AWS and advertising as key reasons for their bullishness.

A digital-looking cloud.

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What analysts are saying

"AMZN's fastest-growing revenue streams are its most profitable & driving margin expansion," said JPMorgan analyst Doug Anmuth in a note to clients this week, according to Barron's. These revenue streams, Anmuth said, are Amazon Web Services and advertising. Specifically, Anmuth estimates these businesses will account for 85% of profits this year. The analyst also reaffirmed a 12-month $2,100 price target for Amazon stock -- much higher than the stock's approximate price of $1,660 at the time of this writing.

Pivotal Research analyst Brian Wieser also expressed optimism for Amazon stock this week, initiating coverage of the stock with a buy rating and a year-end price target of $1,920. Wieser similarly pointed to the company's cloud-computing and advertising businesses as catalysts. Notably, Wieser estimates that Amazon's ad business could grow to $38 billion in sales by 2023, up from an estimate of $9 billion in 2018.

Strong momentum

Investors can get a better idea of Amazon's momentum in these two key areas by looking at the company's recent financial statements.

For the trailing-nine-month period ending Sept. 30, 2018, AWS sales were $18.2 billion, up 48% year over year. Though these sales accounted for just 11.4% of total sales during this period, AWS' operating income was $5.1 billion -- 59% of Amazon's total operating income.

Amazon's advertising business is much smaller than AWS. Indeed, it is lumped into Amazon's "other" segment, where management says it is the segment's primary contributor. But advertising is growing very rapidly, as evidenced by Amazon's 123% year-over-year growth in other revenue in the third quarter of 2018. Wieser estimates that Amazon's advertising sales for the full year of 2018 rose 70% year over year.

Though Amazon's advertising business remains small, with third-quarter "other" revenue accounting for just 4% of total revenue, advertising is already beginning to have a positive impact on Amazon's consolidated gross profit, thanks to its lucrative economics.

With no indication of either of these drivers slowing down, AWS and advertising should continue to represent a larger portion of Amazon's business over time, helping the company's profitability.

Check out the latest Amazon earnings call transcript.