The report also said three Oxfam employees physically threatened a witness.
The former Oxfam official at the centre of a prostitution scandal admitted to paying for sex at his charity-funded residence during an internal inquiry into the allegations, a report released Monday by the British organisation said.
The report also said three Oxfam employees physically threatened a witness in the investigation into alleged sexual misconduct in Haiti following the devastating 2010 earthquake there.
The charity fired fired four staff members for gross misconduct and allowed three others, including former country director Roland van Hauwermeiren, to resign over allegations they hired young sex workers.
The 68-year-old Belgian has denied organising orgies or visiting brothels on the Caribbean island, saying he told Oxfam he had engaged in "intimate relations some three times" at his home but did not pay for these liaisons.
A redacted copy of the 2011 report made public by the charity said Van Hauwermeiren offered to resign after admitting to investigators that he had hired sex workers at Oxfam-funded accommodation.
"During the interview the CD admitted to using prostitutes in his OGB (Oxfam Great Britain) residence," the report said.
During the inquiry, three employees also allegedly threatened a colleague who had been interviewed by investigators after witness details were leaked.
"This incident resulted in three of the suspects... physically threatening and intimidating one of the witnesses who had been referred to in the report," it said.
Details of action taken against the suspects included dismissal for "bullying and intimidation of OGB staff" and misuse of Oxfam computing equipment "through the access and download of pornographic and illegal material".
Oxfam has unveiled an action plan to tackle sexual harassment and abuse, and agreed not to bid for any more state funds until reforms were in place.
It has faced accusations it was not transparent about the scandal, which has led to the resignation of its deputy head and high-profile ambassadors such as Desmond Tutu.
The report said the charity negotiated a month's notice period with Van Hauwermeiren and agreed to allow him "a phased and dignified exit" if he cooperated with the rest of the investigation.
His dismissal could lead to "potentially serious implications for the programme, affiliate relationships and the rest of the investigation", it said.
The report said Oxfam officials had received an email in July that year alerting them to alleged sexual exploitation, fraud, negligence and nepotism during relief efforts.
It concluded that the inquiry found no substantial evidence of fraud, nepotism or hiring underage sex workers, "although it cannot be ruled out that any of the prostitutes were underage".
The charity said it had released the report "to be as transparent as possible about the decisions made during the investigation and in recognition of the breach of trust that has been caused".
Van Hauwermeiren said in a letter published by Belgian media last week that he had not visited any brothels, nightclubs or bars in Haiti.
"There were numerous men and women who tried to get into my house with all sorts of excuses to demand money, work, or to offer sexual services. But I never gave into these advances," he wrote.
In the letter he said he told Oxfam he had sexual relations with an "honourable, mature woman" and did not give her any money, but added he was however "deeply ashamed" of the incident.
Oxfam said it had passed the names of the seven men accused of sexual misconduct to relevant authorities and has shared an unredacted version of the report with the Haitian ambassador in London.
It added it would give a copy of the report to the Haitian government, which has said it would open a probe into the scandal, in a meeting planned for Monday morning.