The evolution of the main sea level pressure patterns built from Rotated Principal Component Analysis (RPCA) over a domain centered on the Mediterranean for the period 1955--1990 is examined. The annual cycle and the interannual variations are analyzed using Singular Spectrum Analysis (SSA) and three methods of spectral analysis, to detect trends and oscillations in the main patterns. The dominant patterns show oscillations characteristic of NAO and SO. This paper shows that NAO and SO seem to be correlated in a band centered in 6--8 years and that SLP behavior over the region is dominated by QBO (which controls the oscillation frequency) while NAO modulates the amplitudes. ¿ 2000 American Geophysical Union