Introduction Advances in technology and science have caused the environmental changes that have become difficult to evaluate and fully comprehend. Oil spillage has a major impact on the ecosystem into which it is being released, immense destruction of the mangrove and rainforest, destruction of crops, farmland, and aquaculture such as fish, periwinkle and drinking water are manifested. Adekunle et al (2003) stated that the Niger Delta region of Nigeria is the hardest hit of environmental destruction arising from oil production. They further stated that people living in the Niger Delta region are faced with health hazards, lack of safe drinking water, to lack of cultivatable land. Pollution of the soil with petroleum derivatives is often observed in municipal soils, around industrial plants and in areas where petroleum and natural gas are obtained (Adam et al., 2003, Clark, 2003). Processing and distribution of petroleum hydrocarbon as well as the use of petroleum product are the main cause of soil contamination, Ayotammo et al. (2006). Changes in soil properties due to contamination with petroleum derived substances can lead to water and oxygen deficit as well as shortage to available forms of nitrogen and phosphorus Wyskowka et al. (2000). Contamination of the soil environment can also limit protective functions, upset metabolic activity, unfavorably affects its function and chemical characteristics, reduce fertility and negatively influence plant production (Gong et al., 1996., Wyszokowiski et al., 2004). According to Adenipekun and Kassim (2006), engine oil affected moisture content in Celosia argentea plant. Some people dump used engine oil anywhere that offers a convenient spot for them to do so. They pour it in wooden areas, in road side ditches, into storm drain, and even into or near creeks or rivers, unware of or unconcerned about environmental damage that results from irresponsible disposal of petroleum products. Disposal of spent engine oil in the big cities in Nigeria has been persistently problematic since many automobile mechanics dispose these oils indiscrimately either in gutters or open lands. This practice adversely affects plants, microbes and aquatic lives (Nwoko et al., 2007; Adenipekin et al., 2008), because of the large amount of hydrocarbons and highly toxic polycyclic aromatic hydrocarbons contained in the oils (Nwoko and Fashemi, 2005). Cowpea (Vigna unguculata) is an annual legume and it is a worm-season crop, well adapted to many areas of humid tropics and temperate zone. It has different types which are often categorizes as erect, semierect, prostrate or climbing. Growth habit ranges from indeterminate to fairly indeterminate. Cowpea is generally tap rooted, it tolerates heat and dry conditions, but is intolerant to frost. Cowpea seeds provide a source of cheap plant protein to humans and livestock. Considering the economic value cowpea plant in the menu of poor people of the world, the present study was aimed at investigating the effects of spent engine oil pollution on proximate composition and extent of accumulation of seeds heavy metals in cowpea.