This study, ‘A Lexico-Semantic Analysis of Helon Habila’s Oil on Water’ examines how meaning is negotiated through the use of some cohesive devices in the text. Previous studies have concentrated on the treatment of environmental issues without much attention paid to how cohesive devices are coalesced in the text to produce meaning. Data for the analysis range from page one to one hundred of the primary text, Oil on Water. Also, the study focused on a qualitative research procedure and adopted Halliday and Hasan’s (1976) cohesion theory as a theoretical model, since this work focuses attention on the deployment of the writer’s mental schemata and use of lexical choices to affect meaning in a text. The study observes that words cannot stand in isolation, as they are related to each other in a text to produce predetermined meaning. This was achieved through the author’s careful use of some cohesive devices such as: reiteration, synonymy, antonymy, hyponymy and meronymy, which improve the textual quality of the text. The study concludes that the author, through the use of cohesive devices, made reading of the text meaningful and easily understood by the reader.