EBay is joining the ever-growing push to deliver goods faster.

The online marketplace today announced “Guaranteed Delivery,” a program that offers eBay customers delivery in three days or less. Guaranteed Delivery will start this summer, the company says, and at launch 20 million of the more than 1 billion items currently listed on eBay.com will be eligible for quick delivery at no additional cost to consumers. “Millions” of the eligible products—but not all—will offer free shipping, the marketplace says.

EBay shoppers will be able to search and filter for fast-delivery products, including items listed that can be delivered in one or two days. EBay’s current search capabilities for shipping options only allow filtering for free shipping and local pickup.

If a guaranteed item arrives late, the buyer has a few options: If the product wasn’t eligible for free shipping, the customer can ask for the cost of shipping refunded; if shipping was free, the customer will receive a $5 coupon toward her next eBay purchase. In addition, the customer can choose to return the item at no cost.

“While the majority of items on eBay already ship within three days or less, as well as for free, Guaranteed Delivery will give shoppers even faster delivery options and the confidence that their items will arrive on time,” Hal Lawton, eBay’s senior vice president of North America, says. 63% of eBay packages are already delivered within three days, the marketplace says. 67% of eBay purchases ship for free.

EBay’s announcement comes soon after two marketplace rivals—Wal-Mart Stores Inc., No. 4 in the Internet Retailer 2016 Top 500 Guide, and Amazon.com Inc. (No. 1)—bolstered shipping offerings to consumers.

Wal-Mart scrapped its ShippingPass program in January and opted instead for a two-day shipping model that doesn’t have annual membership fees. ShippingPass had offered two-day delivery for a $49 annual membership fee, but now the retailer offers the same shipping speed for free to shoppers who purchase at least $35 worth of items. Wal-Mart has more than 2 million products eligible for free shipping.

Amazon in February lowered its free shipping threshold to $35 from $49 for shoppers who are not a part of its Amazon Prime program, which offers customers free two-day shipping among other perks in exchange for a $99 annual fee. Amazon’s $35 free shipping threshold promises all orders will be delivered within five to eight business days. An Amazon spokeswoman in February said there are more than 50 million items available on its site that are eligible for free shipping.

But Amazon’s $35 shipping threshold is not the only competitive edge it has on eBay. Amazon Prime memberships continue to grow. Roughly 49% of U.S. consumers, as of January, live in a household with an Amazon Prime member, according to estimates from Robert W. Baird investment analysts. Approximately 45 million Amazon products are Prime-eligible, analysts estimate.

“Guaranteed expedited shipping has become an increasingly significant deciding factor for e-commerce consumers, with the growth of Amazon Prime setting a high standard for order fulfillment and delivery,” Colin Sebastian, an analyst at Robert W. Baird, wrote in a note to investors after eBay’s announcement. “Guaranteed Delivery is only one step toward meeting the increasing expectations for online order fulfillment, but in conjunction with the company’s broader platform improvements, we believe these changes are a positive sign for the company’s multi-year efforts to remain competitive in the growing e-commerce market.”

For sellers, the program is optional and they’ll need to meet certain standards to participate, which include establishing a proven track record of fulfilling items on time.

The program could rival Amazon’s Seller-Fulfilled Prime service, Sebastian says. Seller-Fulfilled Prime lets selected marketplace merchants flag their product listings as eligible for Prime two-day delivery, but still ship and warehouse the products themselves. Seller-Fulfilled Prime is available only to merchants with a Professional Selling Account ($39.99 monthly subscription) who meet the company’s Premium Shipping requirements and have fulfilled at least 30 Premium Shipping orders over the past 30 days, Sebastian says. Sellers that are eligible to offer Premium Shipping options on Amazon provide customers a delivery day, which includes handling time and shipping speed that sellers set.

“By limiting barriers to entry, eBay has created an attractive low-cost alternative for sellers looking to diversity their online sales channels,” Sebastian writes.