We develop a basic problem in ballistics and impact engineering, conceing the collision of two fluid streams with different widths. The geometrical theory of plane asymmetrical jet formation is presented and a closed form solution is given. The width and flow direction of the outgoing flows are predicted both analytically and numerically as a function of initial configuration of the incoming flows. The predictions are more accurate than the results of other analytic models and in agreement with the experimental data and numerical results over a wide range of flow widths ratio variation.