Four employees were fired and three others, including Roland van Hauwermeiren, resigned before the end of the internal investigation, said Oxfam.
The Times of London's investigation, which was published Thursday (local time), also detailed allegations that Oxfam's country director used prostitutes, as part of the raft of misconduct alleged to have occurred while the organisation deployed to help the reeling island nation recover after a devastating 2010 quake.
One source told the newspaper there was footage of a "full-on Caligula orgy" with women in Oxfam T-shirts.
"The investigation was announced publicly and staff members were suspended pending the outcome".
The report seen by the Times said there had been "a culture of impunity" among some staff in Haiti and concluded that children may have been among those sexually exploited by aid workers.
In early August 2011, it was reported a "small number" of employees were being investigated over allegations of gross misconduct. There are also conflicting reports over whether Oxfam ever reported the incidents to the Charity Commission as it claimed to have done.
According to the British newspaper The Times, Oxfam employees hired young prostitutes in Haiti in 2011 during a mission following the natural disaster that ravaged the country in 2010, killing almost 300,000 people.
In the first wave of humanitarian aid after the quake, Oxfam helped around 700,000 people in the Caribbean country.
The scandal has cast a negative light over Oxfam's work in Haiti. It did, however, state the claims related to abuse of power and bullying and not fraud.
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The report did not detail the precise allegations, nor did it make any indication of potential sexual crimes involving minors.
She said: "We are now engaged with the charity regarding its approach to safeguarding following more recent allegations".
As part of that, we have already asked the charity to review historic safeguarding allegations and its response to them at the time.
"This behaviour was totally unacceptable, contrary to our values and the high standards we expect of our staff", Oxfam, one of Britain's largest charities, said in a statement on Friday.
While Oxfam acknowledged at the time of the staff dismissals that there had been a serious breach of its code of conduct, it reportedly failed to specify sexual misconduct.
An Oxfam spokesman said: 'This was not a cover-up.
According to the Times' repory, groups of young prostitutes were invited for sex parties in Oxfam-paid homes and hotels. Oxfam "did not give us any warning about his unethical behavior, the reasons for his resignation or the results of the internal investigation", the NGO said according to the newspaper.
It also added: "Allegations that underage girls may have been involved were not proven".
"We have a zero tolerance policy for the type of activity that took place in this instance, and we expect our partners to as well".