Instacart employees fulfill orders for delivery at a Whole Foods Market store in Los Angeles.

Whole Foods and Instacart are taking their relationship to the next level.

The $10 billion national grocery store chain is making an investment in the four-year-old delivery startup, according to multiple sources. The size of the deal could not be learned, but sources say the deal is essentially done, barring an unforeseen last-minute change of heart.