Two vessels are scheduled to be delivered to Petrobras at the start 2014.
OOS International will provide the OOS Gretha DP3, which can accommodate 618 people, while sister vessel the OOS Prometheus can accommodate 500 workers.
Both vessels are operated by and under the management of OOS International and will work in the Campos and Santos basins offshore Brazil.
In a statement released by OOS International, founders Leon Overdulve and Jacco van Eerde said the four-plus-four-year charter contract was a significant contract achievement for such a small company.
"We were able to complete this unique transaction over the course of 300 days with the support of the many people who believe in OOS International, including our Brazilian and Chinese colleagues, employees, customers and vendors," they said.
"We are looking forward to a prosperous future.
"The founders of OOS International would like to express their gratitude to He Guoqiang of CIMC Raffles and Minjie Liu of CIMC Capital for their continuing support and trust that this project could happen."