Fifty-six per cent of the attacks were perpetrated by armed men inside family homes, nearly 16 per cent in fields and nearly 15 per cent in the forest, the report said, citing statements by the 4,311 women questioned.
Carried out for Oxfam by The Harvard Humanitarian Initiative, the report spoke of "the stigmatisation that the women are victims of in their families after having been raped and the difficulties they encounter in accessing medical care".
"Fewer than one per cent of the rape victims went to Panzi hospital with their husbands and nine per cent of them were abandoned by their partner," Oxfam said.
Violence escalated in the DRC after many Rwandan Hutus fled to the country following the 1994 genocide in Rwanda.
Since then, the country has been embroiled in widespread conflicts between its army and Rwandan and Congolese militias.
Around 20,000 UN peacekeepers have been deployed in the nation since 1999 to help stabilise it, but thousands are raped each year as sporadic fighting between the various armed groups continues.
Joseph Kabila, the DRC president, has asked the UN to withdraw its peacekeeping mission by 2011, but some UN officials have said they are reluctant to do so.
Krista Riddley, who directs humanitarian policies for Oxfam, said: "This is a wake-up call at a time when plans are being discussed for UN peacekeepers to leave the country.
"The situation is not secure if a woman can't even sleep safely in her own bed at night.'"
The Oxfam report reveals that many of sexual assault cases were carried out by armed men in the presence of the victim's families, including their children.
Susan Bartels, the chief researcher of the Harvard Humanitarian Initiative, said: "Sexual violence has become more normal in civilian life.
"The scale of rape over Congo's years of war has made this crime seem more acceptable."