Amazon Sets New Holiday Records by Chris Morris @FortuneMagazine December 28, 2015, 11:52 AM EST E-mail Tweet Facebook Linkedin Share icons One of Amazon’s most popular features this holiday season could pay off big in the year to come. The online retailer says more than 3 million additional people signed up for its Amazon Prime service in the third week of December—an achievement the company described as “milestone growth” in a statement. While Amazon AMZN has never given any specific numbers when it comes to Prime, the company did offer an official estimate for the first time, saying there are now “tens of millions” of Prime Members worldwide. (Analysts have previously speculated the number to be in the 80 million range.) MORE: Amazon Prime Is Gaining Steam, Posing an Even Bigger Threat to Walmart, Target The company also noted this year saw a record number of items shipped using Prime’s most high-profile benefit—free and reduced-cost shipping. And members in cities where same-day Prime Now delivery is available took particular advantage of that service on Christmas Eve, with the last package—which included dog treats, a Fire tablet, a Lego set, and Stove Top Stuffing Mix—being delivered to a customer in San Antonio, Texas at 11:59pm on Christmas Eve. “Over 200 million more items shipped for free with Prime this holiday, and members doubled their viewing hours of Prime Video compared to last year,” said Jeff Bezos, founder and CEO of Amazon.com. WATCH: For more on Amazon Prime’s competition, watch this Fortune video: The retailer’s electronics unit also got a big shot in the arm in December. The $50 Fire tablet was Amazon’s best selling item during the holidays, with the Fire TV stick being the third biggest seller. Without giving a basis of comparison, Amazon said sales of its devices more than doubled last year’s record-setting number. Among the retailer’s other holiday fun facts: Customers purchased a watch every three seconds this holiday season On Cyber Monday alone, shoppers bought an Adele CD every three seconds Nearly 70% of Amazon’s holiday customers made their purchases via a mobile device Amazon’s good holiday fortune, particularly its surge in Prime subscriptions, could have a longer-term impact on some competitors—notably Netflix NFLX and Spotify. Prime members took greater advantage of the Prime Video streaming service than ever before, doubling their total viewing hours compared to 2014. SIGN UP: Get Data Sheet, Fortune’s daily newsletter about the business of technology. Again, without context, it’s hard to judge how that compares to Netflix viewership, but a Nielsen study in March found that Netflix controlled 36% of households with a streaming service subscription, while Amazon came in at 13%. Amazon says members watched a “record number” of movies on Prime Video in 2015, and its worldwide Prime Music plays during the holiday season were up 350% compared to 2014.