The initial test results of an EPA study in 1989 and 1990 were not conclusive about the value of biostimulation of indigenous microbes and about the use of exogenous bacteria for remediation. In contrast, a later field study in Delaware reached the following conclusions:a. Biostimulation can slow down hydrocarbon removal. b. Exogenous bacteria outcompete indigenous bacteria. c. Biostimulation can accelerate hydrocarbon removal. d. Addition of exogenous bacteria leads to faster hydrocarbon cleanup than biostimulation.