The chief executive of Nasdaq said the stock exchange is "humbly embarrassed" by its bungling of Facebook's hugely anticipated debut as a public company on Friday.
Robert Greifeld told news media there was no indication the delay contributed to the underwhelming performance of Facebook's stock, which ended at 38.23 US dollars - 23 cents above where it began.
Facebook's stock was expected to start trading at 11am but didn't open until 11.32am, and some investors did not learn for hours whether their orders went through.
Mr Greifeld called the social network's first day of trading "successful".
He said late order cancellations caused a glitch, according to reports. He said Nasdaq's board met on Saturday and plans to change its IPO auction process.
The Securities and Exchange Commission has said it is investigating.