A preliminary step towards the construction of self-consistent models for barred galaxies consists in understanding the stellar orbital behaviour in a given axisymmetrical + bar-like potential and, in particular, the influence of various parameters characterizing the bar on the different kinds of possible motions. To do this we undertook a systematic study of the main periodic and quasi-periodic orbits in a two-component mass model: An axisymmetrical part characterized by a rotation curve V(r) = Vo (r/ro)1-δ and a prolate bar-like perturbation whose density distribution is ρ = ρo (1-(x2+z2)/b2-y2/a2)2(a>b). This rather realistic choice for the bar is in agreement with the available photometric data and has several advantages, i.e. all cos(mθ) terms are included and the physical parameters such as the length of the bar a or its eccentricity e are explicitly included in the formulae. The ratio of bar to disk mass measured up to the outer Lindblad Resonance (ε) and the angular velocity (ωs) are also free parameters.