[en] The magnitude of the CKM matrix element V_cb has been measured using B-bar⁰ → D*⁺l^- ν-bar decays recorded on the Z⁰ peak using the OPAL, ALEPH and DELPHI detectors at LEP. The D*⁺ → D⁰π⁺ decays were reconstructed both in particular decay modes and via an inclusive technique. The product of vertical bar V_cb vertical bar and the decay form factor of the B-bar⁰ → D*⁺l^- ν-bar transition at zero recoil _F(1) was measured to be _F(1) vertical bar V_cb vertical bra = (35.6 ± 1.7) x 10^-3. vertical bar V_cb vertical bar is obtained by using Heavy Quark Effective Theory calculations for _F(1). The semi-leptonic branching ratio BR(b → clv) is also used to extract V_cb. The combined result is vertical bar V_cb vertical bar = (40.7 ± 1.9) x 10^-3. The semi-leptonic branching ratio BR(b → ulv) is measured and used to extract the magnitude of V_ub, vertical bar V_ub vertical bar = (4.09_-0.69^+0.59) x 10^-3