Petroleum (2004), by Bessora, is apparently based on a mystery plot : we have to discover the author of the explosion that occurred on the Ocean Liberator, an oil prospecting ship exploring the underwater depths of Mandji Island (Gabon). It soon becomes clear, however, that this « ultra-deep » that attracts human greed is the real epicentre of the novel. Its exploitation secre tes the neo-colonial fossil geography on the surface, but it is also the place where underwater divinities, themselves linked to the spirits of the forests, live. The vertical dynamic that is established in the novel, leading us to sensi tively experience depths which are concrete and animated by energies as material as they are spiritual, thus modifies our perceptions and affects as readers. The elucidation of the enigma is then coupled with a hermeneutic of the territory, unfolding the layers and conflicts of interpretation that are lodged in the imaginations of its inhabitants.