This study examined the eco-physiological effects of soil contaminated with crude oil level (0, 1.0, 2.0, 3.0 and 4.0% w/w) on some growth characters of Persea americana with a view to determining their contributions to yield biomass in 2006 in Asaba, Delta State, Nigeria. The experiment was arranged in a randomized complete block design with four replications. The results showed that soil treatment with crude oil significantly reduced (P<0.05) the performance of the test plant as regards

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... s, number of leaves, leaf area, stem diameter and consequently, dry yield biomass when compared with seedlings grown in soils without crude oil treatment. The results also indicated that the performance of P. americana seedlings grown in soils contamination with 1.0% w/w of the oil was not significantly affected (P>0.05). As from 2.0% w/w, however, performance significantly reduced. This study has demonstrated that soil treatment with crude oil has a highly significant effect of reducing the growth characters of P. americana and consequently, the yield. Based on the findings, the actual level at which oil may begin to damage plants especially P. americana may be 2% w/w contamination, although variations may exist depending on the oil type, stage of seedling development, presence of other pollutants in the soil and other environmental factors.