The big picture: Amazon revealed that during the holiday season, tens of millions of customers started Prime free trials or started paid memberships. More customers signed up for Prime in 2018 than in any other year, we're told.

Amazon's Black Friday and Cyber Monday efforts were well received as net sales increased 20 percent to $72.4 billion in the fourth quarter, the e-commerce giant revealed in its latest earnings report. By comparison, Amazon earned just $60.5 billion during the same three-month period in 2017.

Profit for the holiday quarter checked in at $3.0 billion, or $6.04 per diluted share, versus $1.9 billion, or $3.75 per diluted share, in the year-ago quarter.

For the full year, net sales were up 31 percent to $232.9 billion, compared to $177.9 billion in 2017, while profit climbed to $10.1 billion. In 2017, Amazon earned just $3.0 billion in profit.

Amazon was light on specifics but said that 2018 was the biggest holiday shopping season ever for Amazon devices. The Echo Dot, Amazon's most affordable smart speaker, was the top selling product on Amazon, from any manufacturer, in any category.

Looking ahead to the first quarter of 2019, Amazon expects net sales of between $56 billion and $60 billion, or between 10 to 18 percent higher than Q1 2018.

Lead image courtesy Jeramey Lende via Shutterstock