Two vulnerability index approaches: Standard and a modified DRASTIC, were applied to assess the pollution vulnerability of a coastal plain sand aquifer in parts of southeastern Nigeria. These methods were used to produce vulnerability maps and a groundwater risk map. The results suggest that the aquifer is of moderate vulnerability, while the risk of pollution is high. These maps also identified three vulnerability categories: low, moderate and high. Agreements in the categories of the two methods is found for about 80% of the aquifer area. Generally for this study, 23% of the southern parts of the study area is highly vulnerable and urgent pollution prevention method is necessary. This is due to the high human activity related to oil and gas activities. Comparison of the vulnerability indices with nitrate concentration showed some discrepancies. The study is expected to guide the future development, pollution and management of the aquifer.