Dive Brief:

• Prime Day, Amazon's summer blockbuster sale that last year ran on July 11, stoked brands' and retailers' sales by an average 57%, according to online ad firm Criteo. Amazon's own sales increased 60% during last year's Prime Day, according to e-commerce analytics company Profitero, according to reports emailed to Retail Dive. The day itself delivered $2.9 billion in sales, Profitero said.

• Prime Day's peak sales launched the night before and ran for 30 hours, Criteo's analysis found. Over the week, brands' and retailers' sales rose as much as 30% and, on Prime Day itself, mass merchants' sales surged 124%, Criteo said.

• Desktop sales, rising 71%, outpaced mobile's 31% rise, which Criteo attributed event's timing during the work week. 

Dive Insight:

Amazon's Prime Day, the e-commerce giant's midsummer​ answer to Black Friday, has gained traction, especially among its tens of millions of Prime members.

"'Fabricated' online shopping events like Prime Day are proven to drive significant spikes in traffic and sales volume during times of the year that historically may not have been seasonal peaks," Profitero said in a blog post.

But discounts aren't the only draw. In fact, the most common Prime Day discount rate of 20%-30% actually saw the lowest sales lift; discounts between 10%-20% brought greater sales than the 20%-30% and 30%-40% discount bracket, according to Profitero.

For some items, Alexa-exclusive deals spurred more sales in the days leading up to Prime Day than on the day itself, as Amazon pushed such deals to some customers as early as July 5 before releasing them to all Prime members July 10, Profitero found.

Retailers not selling through Amazon but that anticipated Amazon's timing generated the highest sustained peak, with a 30% increase in sales over the course of the week, according to Criteo.

Prime Day also adds to some products' cache of reviews, widely seen as a major source of the striking level of trust consumers have in Amazon in general. Profitero found that products featured on Prime Day received 100% more new reviews afterward than on products that weren't slated for Prime Day promotion: Those with fewer than 100 reviews prior before Prime Day last year garnered 200% more new reviews.

And Prime Day's effect lingered, according to Profitero. Average daily sales rose 77% following Prime Day and total sales in August last year were 68% higher than in June.