The similarity of the common low values of vertical deformation shapes and of H/V ratios suggests that the new uplift started at Campi Flegrei caldera shares a similar source geometry and mechanism of any recently observed episodes, including the larger ones. In particular, the strict similitude with previous small uplift episodes is strongly constrained by the comparison of H/V ratios between 2000 uplift and the present one. The only difference with previous small uplift episodes [Gaeta et al., 2003; Lanari et al., 2004] is just the slower deformation rate (average of 0.3 cm/month) and the longer duration. Battaglia et al.  showed that the horizontal to vertical displacement ratios were significantly smaller (about one half) during the large 1982–1983 uplift with respect to the 1990–1995 subsidence. Such data are interpreted with two different source geometries and depths of the large uplift with respect to subsidence episodes. The first part of uplift is interpreted as due to overpressure within a penny-shaped crack, located below 3 km of depth [De Natale et al., 2006] which contains magma or fluids of magmatic origin; such overpressure subsequently involves the shallower aquifers (for instance after fracturing of the rock volume between the magmatic fluids and the aquifer). The subsidence is hence interpreted as the water deflation from a prolate ellipsoidal aquifer, located at depths between 1.5–2.5 km, towards the external rocks. The observed H/V ratio for the 2000 and the 2004–2006 uplifts, generally less than 0.37, is indicative of an oblate source (Figure 4c). These observations allow to formulate a model for the occurrence of small uplift episodes, and more generally for the fast ground deformation episodes at Campi Flegrei and similar areas. In fact, in the light of the previously mentioned models, the rather small ratio between horizontal and vertical displacements observed during the small uplift episodes is indicative of overpressure, in the deeper source evidenced by Battaglia et al. , of fluids of magmatic origin. A large uplift episode could then occur when the initial pulse of overpressure, after significantly fracturing the upper rocks, is migrated into the shallower aquifers. Such interpretation is consistent with the observations of Chiodini et al.  that similar peaks of CO2 follow both large and small uplift episodes, with a time lag of several months, thus indicating that uplift episodes are all associated to a significant input of CO2 from below, that is essentially independent from the amount of uplift. A further sharp increase of CO2 flux started some months ago and is still on-going (G. Chiodini, personal communication, 2006). This is in agreement with a model in which all the uplift episodes start with overpressure in a deeper source filled with magma or fluids of magmatic origin, rich in CO2, which is injected in shallower layers. The longer duration of the present episode with respect to previous small uplifts should mean a longer lasting overpressure pulse at the source. Such a model has anyway important implications for eruption hazard because, if the deeper source is filled with magma or reflects new magma arrival, each overpressure pulse brings the system closer to the critical point for rock failure and eruption [De Natale et al., 2001, 2006]. Thus, the about 2.5 meters of residual uplift cumulated since 1969 could be reasonably interpreted as due to the sum of all the positive overpressure pulses, associated both to large and small unrests, in the deep system, which has then been loaded by a considerable additional stress. As a further conclusion, we suggest that the systematic monitoring of the maximum horizontal to vertical displacement ratio using CGPS data is a useful tool for eruption forecasting, because of the strong sensitivity of this ratio to changes in source depth.