The PSV 5000 vessels will be built in Brazil to Damen's design.
The ships will come with diesel-electric propulsion and be chartered to Petrobras for six years, with a six-year option.
They will be built at Wilson Sons' Guaruja yard for WilsonSons Ultratug.
Earlier this week Atlantic Towing (Canada) ordered four ice-strengthened versions of the PSV 500 vessels from Damen.
On delivery in late 2016 they will be deployed to fulfil a 10-year charter from ExxonMobil Canada Properties and Hibernia Management and Development Co (HMDC).