Port-Gentil or Mandji is the second-largest city of Gabon, and it is a leading seaport. It is the center of Gabon's petroleum and timber indu…Port-Gentil or Mandji is the second-largest city of Gabon, and it is a leading seaport. It is the center of Gabon's petroleum and timber industries. The city is located on a delta island in the Ogooue delta. Nearby Cape Lopez is Gabon's westernmost point. As of 2013 census, it had a population of 136,462.