A cobalt electrodeposition composition comprising cobalt ions, and particular leveling agents comprising X1—CO—O—R11, X1—SO2—O—R11, X1—PO(OR11)2, X1—SO—O—R11 functional groups, wherein X1 is a divalent group selected from (i) a chemical bond (ii) aryl, (iii) C1 to C12 alkandiyl, which may be interrupted by O atoms, (iv) an arylalkyl group —X11—X12—, (v) an alkylaryl group —X12—X11—, and (vi) —(O—C2H3R12)mO—, R11 is selected from H and C1 to C4 alkyl. R12 is selected from H and C1 to C4 alkyl, X12 is a divalent aryl group, X11 is a divalent C1 to C15 alkandiyl group.