We analyze the stability of particles at liquid-fluid interfaces as a function of their shape and orientation with respect to the interface plane. To do this we apply the generalized Young's equation, including the line and surface tensions, to the specific shapes of prolate and oblate particles. We show that particles with aspect ratio alpha larger than a critical value (depending on the surface and line tensions) cannot be adsorbed at the interface. The stability of nonspherical particles at interfaces exhibits a rather complex dependence with line tension and orientation. The interplay between these variables results in a destabilization of prolate particles. In general the stability decreases in the order, oblate>sphere>prolate. It is argued that in experiments aiming to investigate the effect and magnitude of the line tension, the optimum experimental choice corresponds to very elongated particles. (C) 2003 American Institute of Physics.