Despite a 55% year-to-date gain for Amazon.com (NASDAQ:AMZN) shares leading up to the e-commerce giant's second-quarter earnings report last week, the company still managed to live up to the elevated expectations that come along with a soaring stock price. Amazon checked all the boxes investors were looking for, including sharp revenue growth, surging profits, another quarter of accelerating sales growth for Amazon Web Services (AWS), and plenty more.

As investors digest Amazon's second-quarter results, here are some key metrics they may want to consider.

Amazon employee with box in an Amazon fulfillment center

Image source: Amazon.com.

1. Net income was $2.5 billion

There was a lot to like about Amazon's second-quarter results last week. But one theme from the report arguably stood out above everything else: surging profitability. Nowhere is this more evident than Amazon's soaring net income. Net income skyrocketed from $197 million in the year-ago quarter to $2.5 billion. 

On a per-share basis, net income was $5.07 -- up from $0.40 in the year-ago quarter.

2. Operating margin was 5.6%

Another way to look at Amazon's impressive profitability is through its widening operating margin. Amazon's second-quarter operating margin was 5.6%,  compared to 1.7% in the year-ago quarter and 3.8% in Q1.

Amazon's operating margin is also improving sharply on a trailing-12-month basis. This key metric has increased from 2% for the 12-month period ending Q2 2017 to 3.5% for the 12-month period ending Q2 2018.

3. There are over 45,000 Alexa skills

Alexa skills, which are essentially apps but for smart voice assistants, have climbed to more than 45,000. This is up by 5,000 in just three months, highlighting the significant momentum Amazon is seeing across its Alexa-enabled devices.

Amazon also notably said that the total number of Alexa-enabled devices -- including third-party devices that use Alexa -- has more than tripled over the past 12 months.

4. AWS revenue increased 49% year over year

Amazon's cloud computing business, Amazon Web Services, saw sales increase 49% year over year to $6.1 billion. This was also up sharply from AWS sales in the prior quarter of $5.4 billion.

Spotlighting AWS' incredible momentum, this was the segment's third quarter in a row of accelerating growth.

5. AWS operating income jumped 79%

Though the bulk of Amazon's net sales are still generated from its e-commerce business, AWS still contributes outsize operating income. AWS operating income was $1.6 billion, up 79% from $916 million in the year-ago quarter. AWS operating income represented 65% of the company's consolidated operating income.

6. Trailing-12-month free cash flow was $10.4 billion

This was up from trailing-12-month free cash flow of $9.6 billion in the year-ago quarter. What's incredible is that Amazon was able to generate over $10 billion in trailing-12-month free cash flow despite a stunning $11.4 billion in capital expenditures during this time frame. In the trailing-12-month period ending one year ago, capital expenditures were $8.2 billion.

7. Amazon's international operating loss narrowed to $494 million

Demonstrating the scalability of its international operations, Amazon's international operating loss narrowed from $724 million in the year-ago quarter to a loss of $494 million in the second quarter of 2018 as the segment's revenue increased from $11.5 billion to $14.6 billion.

With strong growth and improving profitability across virtually all areas of its business, Amazon's second quarter gave investors more reasons to hold on to shares for the long haul.

John Mackey, CEO of Whole Foods Market, an Amazon subsidiary, is a member of The Motley Fool's board of directors. Daniel Sparks has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends Amazon. The Motley Fool has a disclosure policy.