Systems and methods for performing serial crystallography by providing an aqueous suspension of a crystal sample to a T-junction at a first flow rate and providing an immiscible oil fluid to the T-junction at a second flow rate. The aqueous suspension and the oil are combined at the T-junction to produce a co-flow output fluid including a parallel co-flow of the aqueous suspension and the oil in the same output channel. The co-flow output fluid is ejected as a jet stream through a nozzle and the sample flow rate in the crystal sample in the jet stream is adjusted by adjusting the first flow rate of the aqueous suspension and the second flow rate of the oil. By combining the aqueous sample and the oil in this manner, the output of the jet stream can be regulated for compatibility with X-ray free electron laser serial crystallography.