"It was unfortunate despite all the efforts to have plenty of processing capacity," said Costco CFO Richard Galanti during an earnings call Thursday evening.
Black Friday shoppers were greeted with a message stating that the website "is currently experiencing longer than normal response times..."
Despite the outage, Galanti said sales were up in the "very high teens" during the five-day Thanksgiving/Cyber Monday period -- a sign demand could have been better if not for the outage.
"We did leave something on the table there, again we were able to correct it, it took several hours, unfortunately," he added.
The outage raised concerns among the investment community whether Costco needs to improve spending on technology. Galanti made it clear that is not the case.
"Rest assured we're spending a lot of money on things like that."
Costco also got pinched with Thanksgiving occurring a week later this year.
For the fiscal quarter which ended Nov. 24, Costco reported e-commerce sales rose 5.5 percent, down slightly from 5.7 percent during the same period a year ago. Net sales came in at $36.24 billion, up 5.6 percent from $34.31 billion last year.