Results of a comparative study on single-shot surface ablation of commercial optical glasses together with the transient reflectivity enhancement during the process are reported. Three types of optical glasses: Schott’s BOROFLOAT®, BK7 and B270 are ablated by single pulses of 34 fs duration at 800 nm central wavelength of the TeWaTi laser systems at University of Szeged, varying systematically both the pulse energy and the beam diameter on the surface, while recording the reflected signal. The depth and diameter of the ablated holes are characterized ex-situ by a DEKTAK profilometer. Very similar ablation characteristics have been determined: Above the ablation thresholds at 5.84±0.21 Jcm-2 (1.72±0.06*1014 Wcm-2), 6.43±0.56 Jcm-2 (1.89±0.16*1014 Wcm-2) and 5.86±0.31 Jcm-2 (1.75±0.09*1014 Wcm-2) for BOROFLOAT®, BK7 and B270, respectively, both the diameter and the depth of the holes produced show logarithmic increase as a function of pulse energy/fluence until saturating above ~18 Jcm-2. On the contrary, significant differences have been obtained in the time integrated transient reflectivities, with the highest absolute values measured for the BOROFLOAT® glass. Strong spot size dependence has been revealed: The reflectivity increases monotonously with increasing pulse energy for all spot sizes, with decreasing absolute values/slopes with decreasing spot areas. Different reflectivities belong to the same fluence/intensity depending on the actual spot size, consequently the fluence/intensity alone does not define unambigously the characteristics of the plasma. The correct description of the changes in reflectivity requires the specification of the spot size together with the pulse energy/fluence/intensity.