The organisation said on Tuesday it was "extremely grateful" for the bequest from Richard Cousins, who died alongside his fiancee, his two sons and her daughter in the crash on New Year's Eve in Sydney.The sum will be a welcome boost to the charity's coffers after it reported thousands had cancelled donations in the wake of the Haiti sex scandal.
Oxfam was unable to confirm the sum donated, but The Sun reported it to be £41 million.
A "common tragedy clause" was drawn up in his will a year before the accident stating that the charity would be the main beneficiary if he was killed alongside his sons, the newspaper said.
An Oxfam spokesman said: "We are extremely grateful for this bequest of which we have only recently been notified.
-> Giant sinkhole opens up in Yorkshire Sainsbury's car park - fire fighters looking into it"We are working with the family and our board of trustees to identify how the money will be used."
The Compass Group chief executive, 58, former OK! Magazine arts editor Emma Bowden, 48, his sons Will and Edward, 25 and 23, and her 11-year-old daughter died alongside the helicopter's pilot when it plunged into Jerusalem Bay.
The Australian Transport Safety Bureau investigated the crash, which the aircraft's operator said happened after the pilot took a "totally inexplicable" turn some 25 miles north of the Australian city's centre.
A turbulent period for Oxfam began in February when allegations emerged that some of its aid workers had used prostitutes in Haiti, which was reeling from a 2010 earthquake.
Oxfam GB chief executive Mark Goldring told MPs that month that about 7,000 people had cancelled donations in the prior 10 days and corporate sponsors were "reserving judgment".