Abstract. The conservative sequence of a set A under a transformation T is the set of all n ∈ Z such that T n A ∩ A = ∅. By studying these sequences, we prove that given any countable collection of nonsingular transformations with no finite invariant measure {T i }, there exists a rank-one transformation S such that T i × S is not ergodic for all i. Moreover, S can be chosen to be rigid or have infinite ergodic index. We establish similar results for Z d actions and flows. Then, we find sufficient conditions on rankone transformations T that guarantee the existence of a rank-one transformation S such that T × S is ergodic, or, alternatively, conditions that guarantee that T × S is conservative but not ergodic. In particular, the infinite Chacón transformation satisfies both conditions. Finally, for a given ergodic transformation T , we study the Baire categories of the sets E(T ),ĒC(T ) andC(T ) of transformations S such that T × S is ergodic, ergodic but not conservative, and conservative, respectively.