Characterization of the soil microbial community in tallgrass prairie soil and its response to oil-field contamination and remediation treatments was assessed by sequencing 16S rRNA gene sequence libraries derived from soil samples taken at various points in the contamination-remediation-recovery process. Sites that had been disturbed by tilling, contamination by a spill of crude oil or by a spill of oil-field brine were compared. Undisturbed prairie was found to have high proportions of Actinobacteria, a Proteobacteria, and Acidobacteria, lower proportions of Firmicutes, Bacteroidetes, b and d Proteobacteria, a few representatives from a wide variety of candidate divisions, but was noteworthy for the low proportion of g Proteobacteria. Tilling was found to have the least effect on these proportions, sites contaminated with crude oil had decreased representation of Actinobacteria and Acidobacteria and an increased proportion of Firmicutes and g Proteobacteria, especially the latter. Brine-contaminated sites were similar to but more extreme than oil contaminated sites, with the addition of a bloom of Bacteroidetes. Groups that increased in contaminated sites were those containing cultured members able to respond rapidly (r-selected) to an influx of readily degraded hydrocarbons and/or were hypothesized to be more salt-tolerant, while those that decreased grow more slowly (Actinobacteria, Acidobacteria) or may be less tolerant of conditions in brine-impacted soil (Acidobacteria). The application of N-containing fertilizer appeared to lessen the imbalance due to oil-contamination and substantial recovery was seen four years after contamination had occurred. In contrast, the brine-impacted sites showed much less change after three years of treatment.