Dallas, TX (CNN) — UPS has trucks up and running Thursday -- and hopes that holiday cheer may assuage the frustrations of angry customers.
The shipping giant's backlog left some Americans with gifts missing from under the Christmas tree Wednesday.
"We're terribly sorry," spokeswoman Natalie Black told CNN.
FedEx was late with some deliveries as well, but those were "isolated incidents," the company said in a statement Thursday.
FedEx "experienced no major service disruptions in the week before Christmas despite heavy volume. Every single package is important to us, and we will continue to work directly with customers to address any isolated incidents," the statement said.
On Wednesday, FedEx spokesman Scott Fiedler told The Associated Press, "We're sorry that there could be delays and we're contacting affected customers who have shipments available for pickup."
The U.S. Postal Service had no immediate comment on whether it experienced any similar delays.
Spokeswoman Zy Richardson said in an e-mail, "We take great pride in delivering packages for our customers in time for their holiday. ... Our carriers continued to deliver mail on Christmas Day, in many locations, to make sure everyone enjoyed their holiday."
UPS did some package sorting Wednesday, but the company stuck to its plan to make no deliveries on Christmas, giving drivers a break after doing a lot of special deliveries Sunday.
Both UPS and FedEx noted they were handling hundreds of millions of shipments in a compressed holiday shopping time frame, because Thanksgiving was later than usual this year.