There is provided a safe, natural, environmentally sound means of controlling bacterial contamination, corrosion, and souring of oil and gas wells and reservoirs that result from bacteria-contaminated water in a well. In one aspect it is a process for remediation of souring of petroleum reservoirs and coalbeds by adding to the water used in flooding and “fracing” operations an effective amount of virulent (non-lysogenic) bacteriophages (phages) specific for problematic target bacteria. The invention also provides a means for combating loss of effectiveness of bacterial control by staging bacteriophage production and application to control dominant and sub-dominant target bacteria in a community of target bacteria.