U.S. online shoppers looking to stock up for the holidays are finding that virtual store shelves keep getting emptier.

Consumers saw 2 billion out-of-stock messages last month, Adobe Analytics said in a study released Tuesday. Based on total page views that include available goods, the share of out-of-stock messages rose by a third compared with a year earlier, Adobe said in an email. Compared with October 2019, the share more than quadrupled, with much of the dislocation coming during 2020, the first year of the coronavirus pandemic.

The increase underscores how port congestion and a squeeze on trucking capacity are rippling through the consumer economy. While retail giants such as Walmart Inc. and Target Corp. say they’re prepared to handle the holiday rush, the stocking headaches mean that shoppers “will need to be prepared to be flexible,” said Taylor Schreiner, director of Adobe Digital Insights.

The goods shortage isn’t just online, according to a Morning Consult survey last month. That study found that among those who have already started their holiday shopping, more than half reported that a product they wanted to purchase in a store was out of stock. 

At online retailers, electronic goods currently have the highest out-of-stock levels, followed by jewelry, apparel, home and garden, and pet products, Adobe said. 

One result of the bottlenecks is that some people have already started shopping, lured by early holiday deals. Online spending climbed 8% to $72.4 billion in October, Adobe said. Big sellers included Got2Glow Fairy Finder and Bluey toys; PlayStation 5, Nintendo Switch and Xbox Series S consoles; and air fryers.