Influence of biostimulation treatment using composted plant biomass on bacterial diversity of an aged crude oil contaminated soil (ACOCS) was determined using culture-dependent and 16S rRNA gene PCR-DGGE based identification methods. Seven treatment plots were designed and included treatments A (TPA) through G (TPG). Samples were collected bi-weekly from 7 treatment plots designed in situ during a 70-day study period that spanned 10 weeks. Composted (2,500 g each) Water hyacinth (EC), Mexican sunflower (TD) and Bermuda grass (CD) were used as nutrient supplements in 4,000 g of ACOCS in situ. TPA was un-amended while TPB, TPC, and TPD had EC,