Armstrong and Winfrey met in the disgraced cyclist's home city of Austin, Texas, to record the interview yesterday, with millions to watch it tomorrow and Friday.
The 41-year-old was stripped of his seven Tour de France titles by the International Cycling Union (UCI) last year and banned for life after the US Anti-Doping Agency found he had been at the heart of "the most sophisticated, professionalised and successful doping programme that sport has ever seen".
The interview will be broadcast over two nights leading to suggestions of profiteering.
Winfrey said she was satisfied with Armstrong's answers during her interview, adding that she was "mesmerised and riveted" by some.
She said he "certainly had prepared himself". As had she.
"I walked into the room with 112 questions," she said. "In a two-and-a-half-hour interview I asked most of those questions, or at least as many as I could."
Winfrey revealed no lawyers had been allowed at the interview at her request, although Armstrong did have a team of people in the room.
She added that at one point Armstrong asked her: "Will there be a point where you lighten up?"
Asked if Armstrong was contrite during the interview, Winfrey said: "I would rather people make their own decisions about whether he was contrite or not. I felt that he was thoughtful, I thought that he was serious, I thought that he certainly had prepared himself for this moment. I would say that he met the moment."
The UCI said in a statement: "If these reports are true, we would strongly urge Lance Armstrong to testify to the Independent Commission established to investigate the allegations made against the UCI in the USADA decision."
Cycling could be dropped from the Olympic programme if Armstrong implicates the UCI in a doping scheme cover up.
International Olympic Committee member Dick Pound said the IOC might be left with no choice other than to take drastic action if the UCI had acted improperly. "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'."