The charity body says billionaires around the world saw their combined fortunes grow by US$2.5 billion each day in 2018.
The International Development Committee (IDC) said the humanitarian sector's response towards widespread sexual abuse was one of complacency, verging on complicity.
Research showed public trust in charities remained low, with respondents giving the sector a score of 5.5 out of 10 - around the same as in 2016, but down from 2014.
In surveys conducted in five countries last year, Oxfam said it documented what it called "unfair trading practices" by supermarket giants such as setting prices below the cost of sustainable production.
Oxfam Great Britain chief executive Mark Goldring will stand down at the end of the year.
The "Arms Under Control" collective have also called on Spain to stop exporting arms to the Saudi-led coalition fighting Iran-backed Houthi rebels in Yemen, where thousands of civilians have been killed.
Authorities should demand an immediate investigation into all organisations, charities and companies to ensure that no one is made a victim of sexual exploitation.
The trial will examine a US$35 million public contract made in 2009 for the purchase of hundreds of buses to ply routes in San Salvador.
Minister says the government will declare Oxfam GB 'persona non grata' if investigations reveal a link between the funds the aid organisation receives and the sex crimes committed.
Last week, Oxfam unveiled an action plan to tackle sexual harassment and abuse, including creating a new vetting system for staff.
Roland van Hauwermeiren, who led Oxfam's team in Hait, says he had engaged in 'intimate relations some three times' at his home but did not pay for them.
But Mark Goldring's comments drew rebukes on Twitter, including from former interior minister Jacqui Smith.
The disaster relief charity says it wasn't right for them to bid for any new government contracts, given public concern following reports its staff had paid for sex workers.
Baaba Maal says what has happened on a human level is disgusting and heart-breaking.
The government says it 'cannot be partners' with aid groups unless they report every serious incident no matter how damaging it is to their reputation.
Several industry experts warned that the backlash against Oxfam could see charities cover up sex abuse cases for fear of losing support and funding.
A survey conducted also revealed that a existed a 'culture of sexual abuse' in some Oxfam offices, with staff claiming they experienced sexual assault.
Winnie Byanyima, however, hopes to restore the trust and vows to be honest, transparent and accountable in addressing the sexual misconduct.
The Department for International Development (DFID) says the UK-based charity's leaders "showed a lack of judgement" in investigating the matter.
Seven years ago, some Oxfam workers had invited groups of young prostitutes to their guesthouse for sex parties.
On the other hand, the poorest 50% cumulatively did not make any money.
Oxfam said Indonesia's taxation system had failed to play a role in redistributing wealth as it was not collecting nearly as much revenue as it should.