When Greg Greeley and his team flipped the switch on the first-ever Prime Day last year, starting in Japan, they quickly realized their idea to host a major sales event in July would pay off.

"We knew immediately when we turned on Japan and saw the response from Japanese Prime members that we had hit upon something special," Greeley, the vice president of Amazon Prime worldwide, said in an interview Friday.

Heading into the second annual Prime Day this Tuesday, the stakes are higher, as Amazon hopes to make this year's sale even bigger. Greeley spoke with CNET about what consumers can expect from the upcoming event, which is exclusive to its Prime members, and how Amazon made changes in response to consumer criticisms last year. He also offered some insights on what's to come from Prime.

Ben Fox Rubin/CNET

In its more than 10 years of operation, Prime, the $99-annual membership service, has turned into a vital part of Amazon's growth plans, ensuring that millions of customers keep coming back to the online store. The service, which Piper Jaffray estimated has 57 million to 61 million subscribers in the US, now includes unlimited two-day shipping, food deliveries, music- and video-streaming services and cloud storage.

Asked if Amazon was finished adding new features to the program, Greeley said, "Just so we're clear: We are not done. There's more that we can do for Prime."

Here's our Q&A with Greeley:

Q: What can customers expect from Prime Day this year?

Greeley: Our objective is for people to find a fantastic deal on something they want and something they need, and everything in-between. It literally is tens of thousands of deals. Our objective is to make these all the lowest prices we've had this year or the lowest prices we've ever had.

A deal may look weird to one person but be absolutely wonderful to someone else. We try to embrace that at Amazon with our massive collection. I think that's some of the fun of this event.

Amazon

Last year, some customers complained on social media about low inventories, odd or unappealing sales and a hard-to-navigate Prime Day page. Did you think these claims were fair?

Greeley: Social media's a great place to be funny. What we saw was how customers were responding. We saw people buying lots and lot of items. So, it's almost amusing to have someone making a quip on social to say this is something odd or unusual or why would I want this, and then see them selling out. It just shows you the diversity of interests of our customer base.

Admittedly, last year the shopping experience -- it was a little harder to find some of the deals, and we really worked hard this year to help with that.

Last year we said, Well, let's just make sure we have as many deals as Black Friday, or more deals than Black Friday. But we certainly didn't expect it to resonate so well that we ended up having more total sales than Black Friday, just from doing an event targeted at the segment of Prime members. So that was obviously very exciting to us, but it gave us a learning that, Boy, we can lean into all the deals with much deeper inventory. But -- let's be clear -- there will still be items that will sell out.

What can you add to Amazon Prime to improve it in the future?

Greeley: Just so we're clear: We are not done. There's more that we can do for Prime. That means more great content. We're superexcited about how the TV series have performed, and we've been doubling down on those areas. This year we've leaned into great movies. And then faster delivery.

With unlimited shipping, it seems that Amazon encourages impulse buying by its Prime members. How much does Amazon try to cut down on that kind of shopping to save on delivery costs?

Greeley: Our objective is to make sure customers can get items when they need them, and we don't want time to be an impediment to meeting that need, which is why we push on faster [delivery]. We've been investing in the fulfillment network and the supply chain and the transportation capabilities to help make that efficient, so that it isn't as costly.

Of course, the cost of shipping alone for us is more than the $99. You can just go look at the UPS rate card to ship a book. For us, I believe it was $16 to send a 1 pound book, two-day shipping. But we wanted it to be easy. So the idea of unlimited -- we wanted to make that something that customers don't have to worry about. But we'd certainly allow them to go ahead and have an option to "combine my orders." We have another option that says, go ahead and ship it slowly.