The site has been swamped since word of the free offering spread, and it was still blocked for most users at midweek.
The retooled www.Britannica.com received millions of hits Tuesday after the Chicago-based publisher said it was putting all 32 volumes and 44 (m) million words on the Internet for free.
Company officials say extra staff and computer hardware are being deployed to handle the demand. They say they expect the access problem to be cleared up by Wednesday night.
Besides its traditional content, the retooled Web site also includes daily news and links to related sites.
"We have 230 years of editorial experience, and we feel that the Internet provides us with the best possibility yet of reaching the most people," said James Strachan, managing director of the company's Internet division.
The Times newspaper said Wednesday that the move comes amid collapsing sales of the printed version caused mainly by the falling price of personal computers, which are seen as a cheaper and more effective educational tool than a bulky set of books.
The company will continue publishing in book format, with the latest volume to be issued in 2001. It is also available on CD ROM.
The encyclopedia set, whose book set now takes up four feet of shelf space, was first published in 1768 in Scotland. It was introduced in the United States in 1888.
The London-based company, owned by Swiss financier Jacob Safra, said it hopes to increase revenue by selling advertising space on the Web site and offering products associated with its reference material.
"By putting the Encyclopedia Britannica online we can reach 200 million people," Strachan said. "We have looked into this and feel that even though we are supplying a substantial amount of content for free, we have a secure business plan for the future."