Amazon.com (NASDAQ:AMZN) confirmed Wednesday morning that its 2018 Prime Day was a major success, boasting more sales than any other shopping event in the company's history. Of course, the success of last year's Prime Day and the company's overall momentum recently meant investors already expected record sales during the 36-hour shopping event. Nevertheless, it's encouraging to hear the company pulled off yet another big win for Prime Day

Some investors may have had concerns about how the glitches the company experienced during the first hours of Prime Day affected sales. After Amazon's Prime Day began at 3 p.m. ET on July 16, many users were confronted with error messages when trying to shop. But statistics provided by Amazon show the company was still able to smash records.

Here's what investors should know.

Boxes on a conveyor belt in an Amazon fulfillment center

Image source: Amazon.com.

The facts

Sales during the first 10 hours of Prime Day 2018 were not only higher than last year, but increased at a faster year-over-year rate than they did during the first 10 hours of the event last year. For the overall event, which lasted 36 hours versus last year's 30 hours, sales "surpassed Cyber Monday, Black Friday and the previous Prime Day, when comparing 36-hour periods, making this once again the biggest shopping event in Amazon history," Amazon said in its press release about the event. Prime members purchased over 100 million products during the event.

Prime Day 2018 served as a nice catalyst for sales of Amazon-branded devices. Including the 12-hour early access period for members, it was the biggest shopping event ever for Amazon devices. Indeed, the two best-selling products worldwide were both Amazon devices -- the Fire TV Stick with the Alexa Voice Remote and the Echo Dot. Amazon also said Prime Day sales of Echo devices with screens -- the Echo Show and Echo Spot -- hit a record high. In addition, Amazon devices for kids, including kids' versions of its Echo Dots and Fire tablets, did better than in any previous shopping event. Finally, on July 16 specifically, Amazon sold more Fire TV devices and Kindle e-readers than on any other day in the company's history.

A man reading on a Kindle Paperwhite in a car

Amazon Kindle Paperwhite. Image source: Amazon.com.

For some context, Amazon was up against an impressive comparison; Prime Day 2017's overall sales were up 60% year over year. 

Prime memberships continue to grow

Looking beyond product sales, Prime Day 2018 also highlighted the momentum Amazon is seeing with its Prime membership. Not only did a record number of members shop on Amazon during the event, but the company said it added more new Prime members on July 16 than on any other day ever. The company did not give numbers.

Amazon's Prime membership benefits have expanded significantly from the free two-day shipping that made it so popular initially, making it an increasingly effective tool for customer loyalty. Today, Amazon Prime includes access to Prime Video, Prime Music, early access to its Lighting Deals, and more. In addition, Amazon now offers free one-day and same-day shipping in over 8,000 cities and towns.

Amazon's Prime members exceed 100 million globally. And a record number of new Prime membership signups on July 16 shows there's still plenty of room left for Amazon to keep growing its member base.

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.