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interface could, for instance , be offset by low nutrient concentrations Similarly , the favorable nutrient concentrations within certain soils may be offset by the presence of anoxic pockets of contamination within an improperly prepared or managed treatment cell While rate-limiting factors are well known, their interactions with respect to determining rates at which hydrocarbons are biodegraded are not , therefore, it is of significant value to those now doing this work to have been given the opportunity to develop and implement improved treatment protocols Actual experiences under field conditions have lead to a number of meaningful improvements that have resulted in the ability to bioremediate a wider range of contaminants more rapidly and less expensively than in the past Much information has yet to be obtained, however, and efforts continue to acquire additional data on a number of subjects , including the following Physical State of the (Petroleum) Contaminant The surface area available for microbial "attack" has a marked influence on the fate of the petroleum contaminant(s ) . Contaminants may be present as a thin surface film, a stable oil -water emulsion, be entrained within sediments , or associated with suspended particles . • Hydrocarbon utilizing organisms typically position themselves at the hydrocarbon-water interface , a location that assures the maximum access to both the hydrocarbon substrate and water soluble mineral nutrients . Many such microbes also produce surface active agents that emulsify oil , thereby, increasing surface area . This increased surface area also provides additional sites for microbial development and contaminant utilization. Temperature As with other microbial activities , the rate at which petroleum products are degraded is strongly temperature dependent Mesophilic bacteria ( those thriving at moderate temperatures) are generally considered the most prolific degraders Oxygen In their initial attack on hydrocarbons such as petroleum produces , bacteria commonly employ oxygenase enzymes ( i e. chemical compounds that catalyze the transfer of oxygen) . This transfer process requires the presence of molecular oxygen and its availability must be considered as an . important limiting factor for petroleum degradation. When II .