Black Friday has long been one of the busiest shopping days of the year in the U.S. The day after Thanksgiving is the unofficial kickoff to the holiday shopping season and is a favorite for bargain shoppers and retailers alike. Merchants have typically reserved some of their best deals of the year for the shopping extravaganza.

For the past several years, Amazon.com (NASDAQ:AMZN) has sought to usurp that tradition, replacing it with one of its own making. Back in 2015, Amazon launched Prime Day, as a way of showing appreciation for its Prime members on the occasion of its 20th anniversary. The shopping event was billed as "Black Friday in July."

Amazon has just wrapped up its fourth annual event, expanding the shopping hours from 30 hours last year to 36 hours this year, and promising that Prime Day (and a half) would be bigger than ever. Let's take a look at some of the highlights to see if the event lived up to the hype.

A young woman smiling picking an order at an Amazon fulfillment center.

Image source: Amazon.

Off to a "ruff" start

Amazon's website experienced uncharacteristic outages shortly after Prime Day began at 3 p.m. ET on July 16. Shoppers were greeted with pictures of dogs with the caption, "UH-OH. Something went wrong on our end. Please try again." Amazon poked fun at the temporary glitches, saying, "It wasn't all a walk in the (dog) park, we had a 'ruff' start -- we know some customers were temporarily unable to make purchases." 

Despite the initial difficulties, Amazon said it was a record-breaking day and "the biggest global shopping event in Amazon history."

Is there an echo in here?

With more than 1 million deals to choose from, Amazon's sales "surpassed Cyber Monday, Black Friday and the previous Prime Day," according to the company's press release. Amazon sold more than 100 million products during the 36-hour sale, noting that the "best-sellers worldwide were the Fire TV Stick with Alexa Voice Remote and Echo Dot." Including the 12-hour early access sale, this was "the biggest event ever for Amazon devices."

This was also the "biggest event ever for Echo devices with screens," namely the Echo Show and Echo Spot. The company also saw the best sales ever of Amazon devices for kids, like the Echo Dot Kids Edition, Fire 7 Kids tablet and Fire HD 8 Kids tablet. July 16 was also the biggest day ever for Fire TV devices and Kindle e-readers on Amazon worldwide.

This was the first day that Whole Foods was included in the company's Prime Day deals, with hundreds of products on sale. Amazon said the best-selling deal at the healthy grocer was organic strawberries. 

The company also noted that small- and medium-sized businesses selling on the platform "far exceeded $1 billion in sales this Prime Day."

Amazon's Prime Day logo.

Image source: Amazon.

Prime real estate

Most importantly for the company, Amazon said it "welcomed more new Prime members on July 16 than any previous day in Amazon history." While some may have used the 30-day grace period just to get the deals, many will likely stick around. Prime members are among Amazon's most prized customers, as they tend to spend more.

While Amazon has never released detailed figures, Consumer Intelligence Research Partners estimates that the average Prime subscriber now spends about $1,400 annually, compared to just $600 for non-member customers.

Amazon recently revealed that it had exceeded 100 million Prime customers worldwide, with these members enjoying a host of benefits, including free two-day shipping, streaming video and music, and more.

How big?

Amazon was characteristically mum, not providing specific metrics for the event. According to some accounts, Amazon netted $2.4 billion during last year's Prime Day, and early projections were expecting Amazon to surpass $3 billion for this year's event.

No matter how you slice it -- it was another banner day for the Amazon.

John Mackey, CEO of Whole Foods Market, an Amazon subsidiary, is a member of The Motley Fool's board of directors. Danny Vena owns shares of Amazon. The Motley Fool owns shares of and recommends Amazon. The Motley Fool has a disclosure policy.