We extend the Spectral
Decomposition Theorem for hyperbolic sets to singular-hyperbolic sets on
3-manifolds. We prove that an attracting singular-hyperbolic set with dense periodic
orbits and a unique equilibrium of a Cr vector field, where r ≥ 1, is a finite
union of transitive sets; the union is disjoint or the set contains finitely many
distinct homoclinic classes. If the vector field is Cr-generic, the union is in fact
disjoint.