The two-minute recording posted by RadarOnline.com includes segments in which a voice sounding distinctively like the Academy Award-winner is heard telling his then-girlfriend, Oksana Grigorieva, that she is dressing too provocatively and that it would be her fault if she were raped. He uses the N-word at one point, and the recording is laced with his profanity.
Grigorieva recorded the actor-director because she was afraid he might harm her, the website reported. The actor is heard on the recording harshly criticizing Grigorieva for the way she dresses. He accuses her of lying to him about having breast implants.
"They just look stupid," Gibson tells her at one point in the recording. "Keep them if you want to. They look like a Vegas bitch, a Vegas whore."
"You look like a (expletive) bitch in heat, and if you get raped by a pack of (N-word), it will be your fault," Gibson is heard telling Grigorieva. "You provoked it. You are provocatively dressed."
Alan Nierob, a spokesman for Gibson, did not immediately respond to requests for comment.
A phone message left for Grigorieva's attorney, Marci Levine, was not immediately returned.
It is unclear when the recording was made or in what context. It opens with Gibson discussing breast feeding of their now 8-month-old daughter. Toward the end, Gibson indicates he is done with the relationship.
"I don't trust you," the actor is heard saying. "I don't love you. I don't want you."
The recording has shades of another scandal for Gibson -- his use of anti-Semitic and sexist remarks during a drunken driving arrest in 2006. The actor-director later apologized for the statements, which were included in a report by a sheriff's deputy who arrested Gibson that was obtained by celebrity website TMZ.
The former couple have been locked in a bitter custody dispute in Los Angeles. The 40-year-old singer has accused Gibson of domestic violence, and sheriff's officials have launched an investigation.
Records in the court case, which may include the audio recordings, remain sealed.
RadarOnline has been posting text excerpts since July 1 of roughly 30 minutes of recordings of Gibson that she made before the pair broke up in April. Friday's posting was the first time that audio of the encounters had been released.
The recording released Friday is unlikely to be RadarOnline's last word on Gibson. Site founder and Executive Vice President David Perel told The Associated Press that more excerpts of audio that Grigorieva recorded will be posted to the site in coming days.
The site has posted text transcripts that include threats of violence and other racial slurs.
Perel said that RadarOnline has heard "a significant portion" of the recordings. He said the site has verified it is Gibson on the recording.
The website, owned by American Media Inc., which also owns the National Enquirer, did not say how it obtained the tapes. Perel told the AP the site did not pay for the recordings and that they did not come from Grigorieva.
Perel said the site felt it was an important story to publish, despite the disturbing content. He said in some of the recordings, Gibson and Grigorieva's 8-month old daughter can be heard screaming in the background.
The screaming is not present in the audio released Friday.
"We felt it was so newsworthy and so explosive we simply had to report what we heard," Perel said.
Rita Smith, executive director of the National Coalition Against Domestic Violence, said Gibson was exhibiting the behavior of a "typical batterer."
She said there is likely to be significant backlash against Gibson, but whether there are real consequences for the actor remain to be seen.
"I think that people will be similarly outraged for awhile, like they were with Chris Brown, like they were with Alec Baldwin," Smith said. "This is one story out of thousands we hear every day."
Brown remains on felony probation for beating his then-girlfriend Rihanna last year. Baldwin was widely criticized for berating his young daughter in a phone message that was leaked during his divorce from Kim Basinger.
Smith said she hoped the incident would increase awareness of the dire straits of domestic violence shelters around the country, which are facing budget cuts.
"I think it would be better for Mel and for Oksana and for their future partners if there were some real consequences and some real change," she said.