The letter should confirm the traveller’s position and role in the company, written on the company letter headed paper. Should include the traveller’s full passport details, arrival/departure dates, and who will take financial responsibility for the trip, stamped and signed by the relevant ministry. For the Oil & Gas sector it should be stamped and signed by the Angolan Ministry of Petroleum  and Natural Resources (MIRENPET)
Click to see a sample approved letter for work visa from the relevant ministry