Costco continues to chip away at the gold mine that is the precious metals market. The wholesaler is adding Swiss-made platinum bars to its selection.

Costco on Wednesday announced the 1-ounce platinum bars, on sale for $1,089.99 on its website alongside its now-famed gold bars and silver coins. The bars are only sold online, and cannot be delivered to Louisiana, Nevada or Puerto Rico, the company said. Interested buyers will also need a Costco membership, which costs between $65 and $130 a year.

It's no surprise the company has continued to delve into the precious metals market. Gold bars launched at Costco in August 2023, and not even two months later were selling out within hours of a restock. Analysts at Wells Fargo reported in April that Costco was selling as much as $200 million worth of gold bars a month.

"I've gotten a couple of calls that people have seen online that we've been selling 1-ounce gold bars," said Richard Galanti, then-chief financial officer of Costco, on the company's earnings call in September 2023. "When we load them on the site, they're typically gone within a few hours, and we limit two per member."

The value of gold has risen more than 40% in the past year and over 70% in the last five years. But the price of platinum has been a little more rocky in recent years. The value of platinum has risen more than 15% over the past 12 months, though it has dropped more than 8% since topping $1,100 earlier in 2024.

— CNBC's Jeff Cox contributed to this report.