A native of Portugal, Mantas began his professional experience with Hoechst AG in 1986. After a number of promotions to positions of increasing managerial responsibility for various Hoechst business units, he had responsibilities in many regions of the world including Latin America and Asia,as well as at the Hoechst corporate center in Germany.

In 1998, after the demerger of Hoechst’s industrial activities, Mantas became Vice President of Sales for Celanese in EMEA. He subsequently managed global business units for Celanese in Engineering Polymers and Chemicals. In 2007, Celanese divested its oxo chemicals business to Advent International and Mantas became Managing Director of OXEA, the newly formed entity. Under his leadership, OXEA experienced a period of rapid growth and transformation by focusing on specialized oxo derivative segments. After the sale of OXEA to Oman Oil in 2013, Mantas retained his executive role with the company, which is a wholly owned company of the Government of the Sultanate of Oman.