The announcement of Amazon's fifth annual Prime Day brought news of longer selling hours and special events for the "holiday," but it also brought on increased competition from retail rivals. As the sales event kicks off, Retail Dive took a look at the five most-compelling Prime Day stats from experts in the industry.

1. Prime Day sales to bring in $5.8B

   While Amazon doesn't explicitly release data showing revenue generated from Prime Day, Coresight estimates that the event will bring in $5.8 billion this year. This number reflects estimated product sales online, but does not include projected revenue from additional Prime membership sign-ups during the event. Last year, Coresight estimated that the e-commerce giant raked in $3.9 billion in sales during its sales event, according to a report emailed to Retail Dive.

   Coresight raised its guidance for this year's Prime Day due to it being a "bigger event," with more selling hours. Prime Day spans a full two days this year, whereas last year it lasted just 36 hours. The U.S. will account for approximately $3.6 billion in sales, or 62% of total estimated sales, while non-U.S. is predicted to bring in $2.2 billion, according to Coresight. Last year, Coresight estimated U.S. shoppers brought in $2.4 billion and non-U.S. shoppers brought in $1.5 billion.

   The report also points to one of Amazon's online competitors, Alibaba, which last year made $30.8 billion on its own sales holiday, Singles' Day. Coresight estimates that in total worldwide sales, Amazon brought in $277 billion last year, "implying Prime Day contributed around 1.4% of annual sales."

2. For the 1st time, more than half of U.S. households will have Prime Membership for the event

   This year marks the first year that more than half (51.3%) of U.S. households will have an Amazon Prime membership, according to eMarketer data emailed to Retail Dive. In 2019, that number is projected to grow to 65 million users, an increase of 8.6% year over year.

   Amazon's e-commerce sales are also projected to increase 17.7% this year to reach $221.13 billion, per the data. This gives Amazon a 37.7% share of the U.S. e-commerce market, or 4% of total U.S. retail. According to eMarketer, the e-commerce giant holds significant share in several categories in the industry, including books, music and video (67.4%), computer and consumer electronics (46.4%), toys and hobby (44.6%) and health, personal care and beauty (29.6%).

   This bodes well for Amazon considering 56% of consumers are expected to purchase electronics this Prime Day, followed by footwear (46%), beauty and personal care items (39%), and books, music and movies (37%), according to PwC data emailed to Retail Dive.

   "Prime membership is the fulcrum on which Amazon's commerce flywheel spins. No event is more important to attracting and retaining subscribers than Prime Day," eMarketer Principal Analyst Andrew Lipsman said in a statement. "By getting customers to financially and psychological[ly] commit to Amazon, it drives purchase frequency, buying across more categories, and ultimately further entrenches them in the Amazon ecosystem — all right before the all-important back-to-school and holiday shopping seasons."

3. Almost half (41%) of Prime Day shoppers rely on reviews before making a purchase

   In the U.S., 76% of Prime members are expected to shop during the two-day sales event compared to just 63% of members in 2018, according to Profitero data emailed to Retail Dive. That same data shows that 67% of U.K. Prime members will participate in the sales compared to 52% last year. Additionally, Amazon sold more than 100 million products during the sales event last year, which was held in 17 countries.

   According to a separate report from Bazaarvoice, 44% of consumers indicated that recent issues with fake product reviews on Amazon's website will influence whether they participate in the sales event. Thirty-seven percent of consumers said they will be more cautious when shopping on the "Black Friday in July" sales event due to fake reviews and 7% said they wouldn't participate in Prime Day at all. Additionally, 41% of shoppers said reviews were their primary method for making purchase decisions.

4. Amazon saw a 45% spike in traffic last year, but it wasn't the only one

   While the e-commerce giant's sales holiday has garnered widespread popularity since it kicked off five years ago, other retailers have also planned their own sales events around the same time. Walmart unveiled its Summer Savings events, which runs through Wednesday, and Best Buy announced deals of its own in response to Prime Day.

   Target's Deal Days event will take place the same day as Amazon's sales event, and eBay, which is also holding a sales event beginning on Monday, took it a step further by announcing it will offer additional deals if Amazon's site crashes, a jab at the widespread site outage the e-commerce giant experienced last Prime Day. Even smaller players like Ace Hardware are throwing their hats into the ring and launching their own set of deals.

   The race to come out on top with the best deals could bode well for Amazon's competitors, as PwC research reveals customers shop around on Prime Day. Last year, Amazon saw a 45% spike in traffic on the sales holiday, while Costco saw a 27% spike, followed by Apple (22%) and Best Buy (13%).

5. Nearly two-thirds (62%) of consumers say one-day shipping has no influence on Prime Day decisions

   While the shipping race may be heating up with Amazon, Walmart and Target speeding up their delivery times, that may not prove to be as enticing to consumers as retailers may think. According to PwC data, 62% of consumers said one-day shipping will have no influence on whether they complete a purchase on Prime Day.

   But that's not to say the event won't have any impact on consumers' shopping behavior. Fifty-two percent of consumers said they will hold off on purchasing something in anticipation of Prime Day deals, and 60% of shoppers said discounts on the annual sales event are the main reason they originally signed up for a Prime membership.

   Additionally, nearly half (49%) of consumers 35 years old or older said they will research deals prior to the event. That number drops slightly (40%) for consumers younger than 35 years old, but 42% of these consumers will sign up for "watchlists" for deals on the event, while only 35% of consumers over age 35 will do the same, according to PwC.