Amazon (AMZN - Get Report) Prime Day is here, and like last year, Jefferies says the 2019 version of the annual event has the chance to be the Seattle company's biggest sales day ever. 

The first day of last year's Prime Day saw Amazon add more Prime memberships than any other day in company history. And it did so even as it lifted the fee for Prime membership to $119 a year from $99. 

"We expect another solid increase in membership during this year's event as Amazon focuses on furthering international penetration and broadening into older U.S. consumers," analyst Brent Thill said.

"Our view is supported by recent solid momentum (about 50% ex-FX revenue in 2018) as U.S./international Prime penetration remains low at about 30%/<5%, respectively. We estimate every 1 million in incremental Prime memberships adds about 1% to core retail growth." 

Amazon is extending the period of the sale to 48 hours from 36 hours last year, adding to the firm's expectation that this year's event will be its biggest ever.

Last year's Prime Day sale was hurt by glitches that forced some customers to abandon purchases. 

Here is a run down of what you expect on Amazon's biggest shopping day of the year. Amazon is up 0.2% to 2,014.88 Monday morning. 

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