The President Records Act, which requires administrations to archive information, applies to all of Gibbs' tweets and some of the responses he receives, Gibbs told reporters Wednesday.
"What I write and what I tweet is archived as a part of this Presidential Records Act of 1978 because it is work product created as part of my job at the White House," he said. "People that follow me, people that read that, people that re-tweet that, none of that goes into this or is archived as a result of the Presidential Records Act."
"The only thing that would be archived other than what I produce is if you respond directly to me and only me," he added. "It's analogous to sending an e-mail to the White House, which is already archived."
But the disclosure raises one question: Who will want to read Gibbs' tweets decades from now?
Plenty will, some historians say.
"I think anything that comes out of any policy statements created by an administration would be considered to be of value to people in the future," said Susan Cooper, a spokeswoman for National Archives and Records Administration. "How it's created and on what medium it's created is less important than the value of the information."
Gibbs joined Twitter on Saturday, creating an account called PressSec. In his first tweet, he wrote, "Learning about 'the twitter' -- easing into this with first tweet -- any tips?"
A couple days later, he wrote, "wow - in a less than 30 hours almost 17K of you are following - amazing - watch out Kim Kardashian! Thanks to all for the smart tips!"
Gibbs revealed to reporters Tuesday that he is sending out all the tweets himself.
"I was fascinated to watch it," he said. It seemed, as I've said to some of you, an avenue that our voice would be important in," he said. "It's been fascinating to watch just over the few days since I've joined it. I have enjoyed watching you all comment on women's figure skating and ski jumping."
Marc Rotenberg, president of the Electronic Privacy Information Center, whose group has tangled with the White House over its use of social media technologies, said he supports Gibbs' new Twitter account.
"We do think that communication from White House employees should be preserved in any format," he said, adding that his only concern is that the White House could abuse privacy rights with the information it gathers on its communications with people.
Rotenberg said he saw potential value in Gibbs' tweets.
"I think there are important principles underlying these discussions," he said. "It doesn't matter which party is in the White House. It's important to try to understand how decisions were made. That's what it's all about. But sometime trying to apply old principles to new technologies can be tricky."