https://finance.yahoo.com/news/amazon-prime-oneday-shipping-is-money-wellspent-analysts-111713723.html

Since Amazon launched it in 2005, Amazon Prime has changed the way shoppers experience online retail by standardizing two-day fast shipping. And as shoppers’ expectations for fast delivery have evolved, so has Prime itself. Over the years, Amazon has added a number of media services for Prime users to consume, including video and music streaming. Indeed, Prime has become so successful, it now has over 100 million subscribers in the U.S., according to a report published by Consumer Intelligence Research Partners this January. That’s up from roughly 91 million Amazon Prime subscribers in the U.S. at the end of December 2017, according to the same report.

“It can’t be underestimated just how much speed is a driver in e-commerce, and obviously, that’s always been Amazon’s advantage with free two-day shipping,” explains eMarketer analyst Andrew Lipsman. “What's interesting is that, in the last couple of years, other major retailers have started to narrow the gap.”