A refrigeration system can use a flash tank to separate vapor refrigerant from liquid refrigerant. The refrigeration system can include a liquid-refrigerant injection system that can inject liquid refrigerant into an intermediate-pressure location of the compressor. The injected liquid refrigerant can absorb the heat of compression during the compression process. The refrigeration system can include an economizer system that injects a refrigerant vapor into an intermediate-pressure location of the compressor in conjunction with the injection of the cooling liquid. The refrigeration system can incorporate a cooling-liquid injection system that can inject a cooling liquid into an intermediate-pressure location of the compressor.