Amazon celebrated its 20th birthday on Thursday after it reported a surprise second-quarter profit. Amazon credited the profit to continued strength of its cloud-computing business and strong revenue growth both domestically and abroad. That came as it held costs for marketing and package delivery in check.

In a call with analysts, new Amazon CFO Brian Olsavsky said the company would continue to look for ways to keep costs in check while at the same time investing in "things that we think are big and important."

Amazon got a boost in revenue from Amazon Web Services, a suite of products and services offered to businesses by way of remote servers that enable users to access applications on any machine with an Internet connection. Revenue from that business climbed 81 percent to $1.82 billion.

Amazon also said its $99-a-year Prime loyalty program helped drive growth during the quarter. The company won't say how many Prime members it has, but it's estimated to be as many as 40 million, and Prime members typically spend more than other shoppers.

For the current quarter ending in September, Amazon said it expects revenue in the range of $23.3 billion to $25.5 billion.