The South African bank let three people go from its Singapore oil desk and two from London last month, the sources at oil trading desks said.
Those leaving included traders and sales staff.
One source said the move was likely to have been prompted by tough market conditions, but another said the bank was repositioning its capabilities to focus more on African business.
A Standard Bank press officer was not immediately able to comment.
(Reporting by Simon Falush; editing by James Jukwey)