A bounded subset M of a Banach space X is said to be ε-weakly precompact, for a given ε ≥ 0, if every sequenceIn this paper we discuss several aspects of ε-weakly precompact sets. On the one hand, we give quantitative versions of the following known results: (a) the absolutely convex hull of a weakly precompact set is weakly precompact (Stegall), and (b) for any probability measure µ, the set of all Bochner µ-integrable functions taking values in a weakly precompact subset of X is weakly precompact in L 1 (µ, X) (Bourgain, Maurey, Pisier). On the other hand, we introduce a relative of a Banach space property considered by Kampoukos and Mercourakis when studying subspaces of strongly weakly compactly generated spaces. We say that a Banach space X has property KM w if there is a family {M n,p : n, p ∈ N} of subsets of X such that: (i) M n,p is 1 p -weakly precompact for all n, p ∈ N, and (ii) for each weakly precompact set C ⊆ X and for each p ∈ N there is n ∈ N such that C ⊆ M n,p . All subspaces of strongly weakly precompactly generated spaces have property KM w . Among other things, we study the three-space problem and the stability under unconditional sums of property KM w .