According to MANA, The helicopter left Malongo port in Angola's Cabinda province to make the short journey to the Tombua-Landana offshore oil platform but never arrived.
"The helicopter did not reach its intended destination. It was carrying five passengers and one pilot," Chevron said in a statement, adding that one of the passengers was an employee while four others were contractors.
"Extensive search and rescue activities continue for those who remain missing."
Angola competes with Nigeria to be Africa's largest oil exporter, shipping around 1.7 million barrels per day, mainly to Asian markets.