Neither Winfrey nor Armstrong has explicitly confirmed the report. "He did not come clean in the manner that I expected," Oprah told CBS, adding that the two and a half hour interview left them both "exhausted."
The AP cited an anonymous source.
"We are not confirming any specific details regarding the interview at this time," a spokesman for Oprah's network OWN told Reuters.
Meanwhile, Oprah gave little away on Twitter.
Just wrapped with @lancearmstrong More than 2 1/2 hours . He came READY! — Oprah Winfrey (@Oprah) January 14, 2013
However, Oprah said she would appear on CBS television on Tuesday to talk about the interview, which will be broadcast on Thursday.
Armstrong has previously denied using performance-enhancing drugs and has never failed a drug test.
The USADA chief Travis Tygart said the doping scheme in place at the US Postal Service team led by Armstrong was "the most sophisticated, professionalized and successful doping program that sport has ever seen," the AP wrote.
The World Anti-Doping Agency, meantime, responded to the news of Armstrong's admission by saying that he must confess under oath to seek a reduction in his lifetime ban from sports for doping.
According to the New York Post, Armstrong hoped to return to competition in recognized triathlon events.
Hoiwever, the WADA — while it "read with interest media reports suggesting a television 'confession' made by Lance Armstrong" — said:
"Only when Mr. Armstrong makes a full confession under oath — and tells the anti-doping authorities all he knows about doping activities — can any legal and proper process for him to seek any reopening or reconsideration of his lifetime ban commence."
The speculation Armstrong will confess to doping during his appearance on Oprah is big news in France.
Public comment on the news daily Le Figaro's website reflected widespread public outrage over the revelations in a country where cycling is one of the most popular sports and the Tour de France is a hallowed national institution.
Many believe the Oprah appearance is part of a cynical strategy by Armstrong to rehabilitate his public image in the United States and minimize the risk of legal action that could might see him facing criminal charges or hefty demands for compensation from sponsors.
"It's unbelievable how this cheating pseudo-champion has been able to hoodwink cycling fans," posted one reader. "Of course the international cycling bodies are not whiter-than-white in this ... professional sport has been polluted by money."
The sports daily L'Equipe, which has been at the forefront of the allegations since the mid-2000s, ran several Armstrong-related pieces on it website focusing on the legal implications of a confession.
Le Figaro also carried a long story on the prospect of a confession that looked at the possibility that the Armstrong-like shamed Olympic sprinter Marion Jones could face jail time.
However the paper quoted Thibaut de Montbrial, who has been involved in Armstrong-related cases in the past, as saying he thought that was unlikely.
"Armstrong is a strategist. He won't run the risk of going to prison. This is a very unusual sportsman, he's always acted like a businessman, a strategist," the paper quoted de Montbrial as saying. "All through his career he has calculated and planned every step."
From its headquarters in Switzerland, the International Cycling Union said it would not be commenting until Armstrong's interview airs. Media reports have suggested that Armstrong has done a deal with authorities to testify on UCI role in doping in order to avoid tougher penalties.
"The UCI notes the media speculation surrounding the interview and reports that he has finally come clean and admitted doping during his cycling career," it said in a statement. If these reports are true, it added the Union "would strongly urge" to testify into the independent commission set up to investigate the UCI's role in the affair.
It's possible cycling could be exiled form the Olympics if Armstrong reveals that UCI had a part in a doping cover up, International Olympic Committee member Dick Pound told Reuters on Tuesday.
"The only way it is going to clean up is if all these people say 'hey, we're no longer in the Olympics and that's where we want to be so let's earn our way back into it,'" Pound said.
More from GlobalPost: Lance Armstrong admits to doping during Oprah interview (UPDATE)