The southern Aegean seafloor exhibits clear evidence of internal deformation (stretching) as shown by tectonics, seismology and space geodesy. We use an analog three-layer laboratory experiment of sand, silicone putty and honey to investigate the deformation of the southern Aegean lithosphere. The model is installed in a box and confined by a vertical wall. We open a gate in the wall and observe the deformation of the two upper layers due to buoyancy forces. The general pattern of the deformation of the southern Aegean is found in the analog model. We observe the formation of an arc spreading outward with time, the extension is radial in the inner part, but parallel to the arc in the external part and of comparable importance. At both ends of the gate we observe strike-slip motion (dextral in the western part, sinistral in the eastern part). Rotation (clockwise in the western part, counterclockwise in the eastern part) of up to 40¿ is seen on both sides of the gate but is also present, with a smaller amplitude, far in the internal region, partially due to distributed shear. The spreading is associated with the thinning of the two upper layers and affects a region of dimensions comparable to the length of the free boundary. This spreading does not propagate inward with time. Some pieces of material located near the active boundary remain undeformed during the experiment. ¿ 1997 American Geophysical Union