De Haas-van Alphen and Shubnikov-de Haas oscillations have been studied in the quasi-two-dimensional organic superconductor κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br at different magnetic field orientations with respect to the conducting layers. At ambient pressure, the oscillation frequency spectrum reflects the Fermi surface topology predicted by hand structure calculations. Estimates of the spin g-tactors indicate discrepancies either in the g values or in the conformity to the Lifshitz-Kosevich formalism of charge carriers on different parts of the Fermi surface. In contrast to the standard theory, simultaneous de Haas-van Alphen and Shuhnikov-de Haas experiments reveal a beating behavior of the magnetic breakdown oscillations in the de Haas-van Alphen but not in the Shubnikov-de Haas signal within the studied field range.