It used to be that with dedication and a good pair of scissors, one grocery shopper could get the same coupons — and cheap prices — as another.

Now going to the grocery store is becoming a lot less egalitarian.

At a Safeway in Denver, a 24-pack of Refreshe bottled water costs $2.71 for Jennie Sanford, a project manager. For Emily Vanek, a blogger, the price is $3.69.

The difference? The vast shopping data Safeway maintains on both women through its loyalty card program. Ms. Sanford has a history of buying Refreshe brand products, but not its bottled water, while Ms. Vanek, a Smartwater partisan, said she was unlikely to try Refreshe.

So Ms. Sanford gets the nudge to put another Refreshe product into her grocery cart, with the hope that she will keep buying it, and increase the company’s sales of bottled water. A Safeway Web site shows her the lower price, which is applied when she swipes her loyalty card at checkout.