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Google today called for San Francisco Bay Area residents to sign up for six months of free, unlimited same-day delivery of purchases from national and local retailers.

The company is calling the program “a new experiment” — more specifically, it’s named Google Shopping Express.

Users can browse in an online storefront and then select a delivery window for a “Google courier partner” to arrive at their home later that day.

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Google has not yet had a home run from its many shopping, wallet, commerce and payment efforts. But same-day delivery is looked at as a sort of holy grail for online retail, since it can bring near-instant gratification to shoppers. As such, Amazon, eBay, Walmart and startups like Postmates are already trying it. Users who sign up for Shopping Express are told they may be selected through a gradual rollout “over the coming months.”

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Participating retailers include national brands like Target and Walgreens and local brands like Blue Bottle Coffee and Palo Alto Sport Shop and Toy World.

News of the service was first reported earlier this month by TechCrunch.