We classify nef vector bundles on a projective space with first Chern class three over an algebraically closed field of characteristic zero; we see, in particular, that these nef vector bundles are globally generated if the second Chern class is less than eight, and that there exist nef but non-globally generated vector bundles with second Chern class eight and nine on a projective plane. 0 → O(−3) → O(−2) ⊕5 → O(−1) ⊕10 → O ⊕r+6 → E → 0; (9) c 2 = 5 and 0 → O(−1) ⊕2 → O(1) ⊕ O ⊕r+1 → E → 0; (10) c 2 = 5, n = 3 or 4, and 0 → O(−2) → O(−1) ⊕5 → O ⊕r+4 → E → 0;