High-pressure-driven "twin-jet sprays" were studied in connection with development work for new injectors for combustion engines. For this purpose, a test rig was set up that allowed two high-pressure liquid jets to be produced that could collide at a pre-given distance and impingement angle. From the crossing regions of the investigated twin jets, very fine sprays emerged. Their properties were investigated for different orifice diameters, different impingement angles, and different jet velocities. The experimental results obtained with the test rig are summarized in this paper. They are compared with corresponding theoretical results obtained using theories of spray formation by twin jets available in the literature. The agreement regarding the measured particle size turned out to be poor for high supply pressures and it was therefore decided to develop an extended theory to describe the experimentally obtained data. The resultant theory is summarized and some predicted results are compared with corresponding experimental data. Good agreement was achieved between the authors' experimental and corresponding theoretical results. Hence a theory resulted from this work for predicting the droplet size of twin-jet sprays at high pressure. The applicability of the theory at low pressure was also achieved by adding some experimental findings.