Inmates caused £171,000 worth of damage as they ran rampage at the £160 million super-jail.
Security firm G4S, which runs the prison in Featherstone, and the Ministry of Justice say the staffing level on the day was 'comparable' to those at public sector jails.
The prisoners took over two levels of Cedar wing at 5pm on January 4 last year, barricading themselves inside and putting glue in locks to prevent them from working. Frances Crook, chief executive of the Howard League for Penal Reform, said officers needed to be highly-trained.
She said: "It is not just a case of number crunching, it depends on the environment. If you have got violence, bullying, attempted suicides and drug problems, which we know there have been at Oakwood, then you need staff with those expertise and knowledge. For there to be a riot with two officers covering 59 prisoners it makes you question what they were doing."
Prisoners threw TVs and even tried to tunnel out as they ran amok. Windows were smashed and booby-traps set, while a pool table was tipped over and large flat-screen TVs thrown down the stairs.
A 62-strong riot team with dogs was needed to restore order. Six prisoners were given sentences for their roles in the riot last week.
A Prison Service spokesman said: "Staffing levels across the estate are strictly risk-assessed and we will always ensure that there are enough staff to deliver safe and effective prison regimes.
"Oakwood prison staffing levels are comparable to those in similar prisons in the public sector."