Amazon continues to increase its speed of shipping packages to Prime members, as more than half of orders last quarter in the top 60 largest U.S. metros arrived the same or next day.

That is spurring the company to double the number of same-day delivery sites “in the coming years,” Worldwide Amazon Stores CEO Doug Herrington announced Monday. Same-day delivery is already available in more than 90 U.S. metropolitan areas.

The move will solidify Amazon’s lead in the $1.4T online shopping market, Bloomberg reported. The 1.8 billion units Amazon has delivered to Prime members in the U.S. with one-day or same-day delivery this year is up about fourfold from the same period in 2019, the article states.

Amazon’s announcement did not detail how many same-day warehouses it has, but Bloomberg reported that doubling the number would probably entail building dozens of new facilities.

More, smaller facilities with more efficient pick-and-pack systems allow Amazon to speed up deliveries, Herrington’s announcement said. The country is broken into eight interconnected regions, and more than 76% of orders come from within the customer’s region, he said.

“What’s changed is the product is traveling fewer miles and experiencing fewer handoffs between the time you place an order and the time it gets to your door,” Herrington said.

Amazon is scheduled to report its second-quarter earnings results Thursday. Investors are increasingly concerned about the margin-eating costs of packing and delivering orders, Bloomberg reported, but some will probably be encouraged that Amazon can increase sales and make online shopping more efficient.

Amazon captures one-third of all spending in the U.S. e-commerce market, which is about six times more than its closest competitor, Walmart, Bloomberg reported using Insider Intelligence estimates.