The aid group said it would create an independent commission which will have the power to access records and interview staff in a bid to stamp out abuse and impose stricter controls on employees.
"We are going to create a vetting system," Winnie Byanyima, executive director of Oxfam International, told the BBC.
"Im really inviting anyone who has been a victim of abuse by anyone in our organisation to come forward."
The new plan comes a week after revelations that Oxfam staff used prostitutes while working in Haiti following a devastating 2010 earthquake and a wave of subsequent allegations of sexual misconduct.
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The charitys deputy chief executive Penny Lawrence has resigned and three Oxfam global ambassadors including South Africas Archbishop Desmond Tutu have quit their roles as a result of the scandal.
"What happened in Haiti and afterwards is a stain on Oxfam that will shame us for years, and rightly so," Byanyima said, adding: "From the bottom of my heart I am asking for forgiveness."
But Roland van Hauwermeiren, Oxfams director in Haiti at the time and one of the three who resigned from the charity, dismissed the allegations.
"I have never been into a brothel, a nightclub or a bar in that country," the 68-year-old Belgian national said in a four-page letter published on the website of Belgian VTM News.
"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 said.
"This was with an honourable, mature woman, who was not an earthquake victim nor a prostitute. And I did not give her any money," he said, adding that he was however "deeply ashamed" of the liaison.
In comments to reporters at the newspaper Het Nieuwsblad, who tracked him down in an unidentified town on the Belgian coast, Van Hauwermeiren said there were "lots of lies and exaggerations" in media reports.
The charity has denied covering up the Haiti affair, which has prompted a drop in donations and led the British government to threaten to cut funds to organisations which try to hide sex scandals.
The charity admitted Thursday it rehired one of those sacked in Haiti just months later and is now checking whether any complaints were subsequently made.
Gurpreet Singh worked as a consultant in Ethiopia from October to December 2011, a decision Oxfam said was "a serious error and should never have happened".
The charity on Friday said it was also investigating allegations of sexual misconduct at a hotel in the Philippines after a destructive typhoon in 2013.