Business under the prevailing economic environment, have to be efficient to survive. Faced with diminishing markets, businesses have had to compete more aggressively with one another to attain acceptable sales volumes and market share. This development has brought the marketing function to the fore front of business activity in the country. Businesses now find it necessary to fashion out strategies and marketing programmes aimed at growth, market retention or simply, their continued existence as a going concern. In performing this function at a time when costs have become more critical than ever before, marketing managers have to ensure that resources available to them are effectively utilised to achieve set objectives. This study is an attempt to investigate the application of the concept of market segmentation in marketing petroleum and allied products by the major petroleum marketers with Unipetrol Nig. Plc, a major marketer as a case study. Three petroleum products were considered for the study viz: premium motor spirit (PMS), Diesel and engine oil - a lubricant. The study reveals the various segmentation strategies/approaches unipetrol employs in marketing the three products under study. Two of the products: premium motor spirit (PMS) and Diesel has almost the same segmentation strategy while Engine oil-a lubricant, has a different segmentation strategy. The marketing strategy used for premium motor spirit and diesel is the undifferentiated strategy while differentiated strategy is used for engine oil. Unipetrol Nig. Plc uses two main criteria to select market segments for the three products under study, these are recheability for premium motor spirit and diesel and size of the market is used for engine oil. Geographic characteristics is the basis for market segmentation for the three products while the segmentation strategy for premium motor spirit and diesel in market orchestration and that of engine oil is product differentiation. Market segmentation has enabled Unipetrol Nig plc witness increased total sales leading to a satisfactory sales performance over the last five years.