DoorDash has agreed to buy grocery delivery company Instacart for about $17 billion in cash and stock, the companies said Thursday. The deal would combine two of the largest U.S. delivery platforms and is expected to face a lengthy antitrust review.

DoorDash will pay $65 per share for Instacart, which is formally known as Maplebear Inc. That is a 26% premium to Instacart's closing price on Oct. 22, the last trading day before media reports of a possible deal surfaced.

It is the largest acquisition in DoorDash's history.

At least 75% of the purchase price will be paid in cash, with DoorDash stock making up no more than 25%.

Instacart shareholders can choose one of three forms of payment for each share:

All stock: 0.3372 DoorDash shares

Mixed: $48.75 in cash plus 0.0843 DoorDash shares

Stock elections will be prorated if too many shareholders choose DoorDash shares.

DoorDash said it will fund the cash portion with cash on hand and new debt. JPMorgan Chase provided a commitment for a 364-day bridge loan. The deal does not depend on financing, and DoorDash said it aims to keep its investment-grade credit ratings.

'Grocery is one of the hardest things'

DoorDash co-founder and Chief Executive Tony Xu said the deal would strengthen the company's push into grocery delivery.

"Grocery is one of the hardest things to get right online," Xu said in a statement. He added that Instacart had spent years learning how to serve grocers well.

"It's still early innings, but we know that when more people shop local, more dollars........

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