Barred Galaxies:Studying the chaotic and ordered nature of orbits

7 pages, 3 figures, in the 7th Astronomy Conference of the Hellenic Astronomical Society, Kefallinia, Greece, (in press)The chaotic or ordered character of orbits in galactic models is an important issue, since it can influence dynamical evolution. This distinction can be achieved with the help of the Smaller Alingment Index - (SALI). We describe here briefly this method and its advantages. Then we apply it to that case of 2D and 3D barred galaxy potentials. In particular, we find the fraction of chaotic and ordered orbits in such potentials and present how this fraction changes when the main parameters of the model are varied. For this, we consider models with different bar mass, bar thickness or pattern speed. Varying only one parameter at a time, we find that bars that are more massive, or thinner, or faster, have a larger fraction of chaotic orbits