Between them, the funds made a profit of £2.9bn over a five-year period from 2011 to 2017, and paid £13.5m in taxes.
Nothing was paid in corporate tax by the funds, which have been registered in offshore territories for the past six years.
ESSU director Dexter Whitfield told BBC that offshore companies were profiting massively from buying public assets, having annual returns as high as 28% from their PFI investments.
Calling PFIs a “private sector profit machine”, Whitfield said that if the government had built public infrastructure through public investment and ran it through in-house services, the whole “edifice” would not be happening.
Research from the ESSU showed 12 offshore infrastructure funds had equity in 547 PFI/PPP projects, amounting to 74% of all 735 PFI/PPP projects in the UK.
Additionally, it was found that 45.4% of all 735 current projects was owned by 9 offshore infrastructure funds.
Projects in education and health accounted for two-thirds of PFI/PPP projects which offshore infrastructure funds had 50% to 100% project equity in.
Last month, Labour pledged to nationalise PFIs and said they would review future PFI contracts.