  This paper deals with the problem of location and existence of limit cycles
for real planar polynomial differential systems. We provide a method to
construct Poincar\'e--Bendixson regions by using transversal conics. We present
several examples of known systems in the literature showing different features
about limit cycles: hyperbolicity, Hopf bifurcation, sky-blue bifurcation,
rotated vector fields, \ldots for which the obtained Poincar\'e--Bendixson
region allows to locate the limit cycles. Our method gives bounds for the
bifurcation values of parametrical families of planar vector fields and
intervals of existence of limit cycles.
