Virginia Gov. Tom Kaine spread word he had been ruled out and Sen. Evan Bayh of Indiana was told he was not Obama's choice, according to party officials.
The normally loquacious Biden maintained a low profile as associates said they believed - but did not know - that he would be tapped. They added they had been asked to stand by in case their help was needed.
Additionally, several associates of Obama - including some at his campaign headquarters in Chicago - said they believed Biden was the choice, though they cautioned they had not been told directly.
Compounding the mystery, conservative Rep. Chet Edwards of Texas emerged - however briefly - as a contender.
Former first lady Hillary Rodham Clinton's chances remained uncertain on a day filled with them. Senior aides said the Obama campaign had never requested financial or other records from her.
Kansas Gov. Kathleen Sebelius rounded out the roster of likely contenders - a list that did not take into account any surprises that Obama might harbor.
"No, no, no, no, no, no, no, nooooo," Sebelius told reporters who asked for her latest thoughts on the months-long search.
Three days before Democrats open their convention in Denver, officials said the Obama campaign had taken the trouble to print material bearing the names of several potential ticket mates. The result was to minimizing the significance of a report that one company was churning out signs bearing Bayh's name. >
In an interview that aired Friday on CBS News' The Early Show, Obama talked about the process.
"Obviously, the most important question is: Is this person ready to be president?" he said. "Can this person help me govern? Are they going to be an effective partner in creating the kind of economic opportunity here at home and guiding us through some dangerous waters internationally?"
And, he added: "I want somebody who is going to be able to challenge my thinking and not simply be a 'yes person' when it comes to policymaking.
( for the exclusive interview with Harry Smith).
Obama told reporters on Thursday he had made his choice, and aides used the prospect of a text-message announcement to try and attract additional supporters by soliciting their cell phone numbers and e-mail addresses.
Even that became occasion for intrigue.
Late Friday, several officials said the text message announcement would be distributed Saturday morning, a few hours before a scheduled rally at the Old State Capitol in Springfield, Ill., where the Democratic ticket would appear for the first time.
Hundreds of miles to the west, carpenters, electricians, sound stage gurus and others transformed the Pepsi Center in Denver into a made-for-television convention venue.
Tucked away in one corner were thousands of lightweight rolled cardboard tubes, ready-made handles for signs bearing the names of the Democratic ticket - once the identity of Obama's running mate was known.
Edwards, whom House Speaker Nancy Pelosi had touted for running mate, told The Associated Press in Waco, Texas, "I have had interactions with the Obama campaign over the last several months but I will not get into details."
VP Hot Sheet: CBSNews.com Tracks Veepstakes Buzz:
Kaine, a moderate governor from a swing state, boarded a private plane at a small airport for a flight that aides said would take him to suburban Denver.
Bayh, a second-term senator, attended tennis camp with one of his sons, while Biden, the chairman of the Senate Foreign Relations Committee, evidently spent the day at his home in Delaware.
Clinton is apparently not under serious consideration and spent the day at the New York State Fair in Syracuse. Sources say she was not vetted by the campaign, but her supporters are still holding out hope Obama will pick her, reports CBS News correspondent Dean Reynolds.
"My answer to any question about the subject that I think you're referring to is that all inquiries should be directed at Senator Obama's campaign," said Clinton, the former first lady who came close to capturing the nomination in the primaries of last winter and spring.
Despite the advice, neither Obama nor his aides were saying.
Among those believed in the running, Edwards and Biden fit the mold of running mate with experience in defense or foreign policy - areas in which Obama is rated relatively poorly in the polls compared with Republican.
Clinton's credentials were forged in the primaries and caucuses where she ran a close second to Obama in the battle for the nomination. She maintains a loyal following among Democrats, many of whom have yet to swing behind the man who defeated her.
There was no shortage of other speculation, ranging from GOP Sen. Chuck Hagel of Nebraska, who traveled with Obama to Iraq and Afghanistan, to Massachusetts Sen. John Kerry, the 2004 Democratic presidential nominee, to Democratic Sen. Chris Dodd of Connecticut.
The emergence of Edwards as a possible selection was the surprise of the day.
Edwards is a favorite of Pelosi, who praised his "extraordinary credentials" on ABC's "This Week" on Aug. 3 and said: "I hope he will be the nominee."
One Democratic official with knowledge of the conversation said Obama told Pelosi recently that she would be pleased with the choice. Other Democratic officials said he was on the short list. All spoke on the condition of anonymity because they were not authorized to discuss Obama's selection process. .
Several GOP officials said Friday that Arizona Sen. McCain, Obama's Republican rival, had not settled on a running mate - nor offered the job to anyone - although former Massachusetts Gov. Mitt Romney and Minnesota Gov. Tim Pawlenty were under serious consideration. It's likely McCain will wait to see who Obama selects before picking his running mate.
Officials said the campaign also was preparing for an "unconventional" nominee, an indication that oft-mentioned former Pennsylvania Gov. Tom Ridge, an abortion-rights supporter, or Connecticut Democrat-turned-independent Joe Lieberman still could be in the running. That category also could include non-politicians whom McCain deeply admires, such as Gen. David Petraeus, the top U.S. commander in Iraq.
Two officials close to Romney said he had not been offered the job. Pawlenty batted away questions Friday in a CNN interview, saying, "I'm sure he'll make a wonderful choice for our party and for our country, and we'll just have to wait until next Friday to find out the answer to those questions."
The GOP convention begins Sept. 1 in St. Paul, Minn.