NEW YORK – A sharp increase in online shopping this holiday season resulted in broken delivery promises, causing many empty Christmas stockings, the Wall Street Journal reports.

The late surge in activity suggests companies do not fully understand consumers’ buying patterns during the Internet era.

Amazon, Kohl’s and Walmart were among retailers who promised to deliver items before December 25, only to see holiday packages landing short of their promised destinations on Christmas Day.

"The volume of air packages in the UPS system did exceed capacity as demand was much greater than our forecast," a UPS spokesperson said. Consumers also reported missing deliveries from FedEx.

E-commerce represents roughly 6% of overall U.S. retail sales, according to the Commerce Department. This holiday season, online purchases will represent nearly 14% of sales, the National Retail Federation said.

UPS sent notifications to some Amazon customers that shipping delays were the result of delays by Amazon, a claim that Amazon disputed.

"Amazon fulfillment centers processed and tendered customer orders to delivery carriers on time for holiday delivery," said an Amazon spokesperson. "We are reviewing the performance of the delivery carriers."

Some retailers blamed the problem on a decrease in the number of shopping days between Thanksgiving and Christmas, which compounded last minute shopping.

According to Forrester Research analyst Sucharita Mulpuru, about 15% of online shoppers miss their promised pre-Christmas delivery window. And with online shopping increasing, the volume of errors is likely to increase, even if the percentage doesn’t. 

"Retailers think they can take orders up to the last minute, but they just can't pick and pack fast enough," Mulpuru said.