Amazon.com, the largest online retailer, offered $20 gift cards and refunds on shipping charges after United Parcel Service said overwhelming volume left it unable to deliver some packages by Christmas.
Amazon cited failures in UPS' transportation network in messages to customers, saying its own fulfillment centers processed customers' orders in time for holiday delivery.
"We are reviewing the performance of the delivery carriers," Mary Osako, an Amazon spokesman, said in an email.
UPS, the world's largest package-delivery company, said in a service update on its website that the volume of air packages exceeded its capacity immediately preceding Christmas.
Read tomorrow's Arkansas Democrat-Gazette for full details.