Aim: To evaluate the efficacy of Revo-S and Reciproc R40 NiTi files in preparation of oval root canals using Cone Beam Computed Tomography (CBCT). Methodology: Forty extracted single rooted premolars were divided into 2 groups (n=20). Group 1 (R-S) were prepared with Revo-S up to size #40/.06. Group 2 (R40) were prepared to the same size with a single file R40. Pre- and post-instrumentation CBCT scanning was done. Calculated parameters were: increase () in canal volume and surface area. Transportation, centering ability, and untouched canal areas were tested at 3, 6, 9 mms axial sections. Statistical analyses were made using Mann-Whitney U and Friedman’s test (P ≤ 0.05). Results: Significant increase in volume (P =.000 and P=.003 for R-S and R40 respectively) and surface area (P =0.048 and P =0.038 for R-S and R40 respectively) was found for both instrumentation kinematics with no significant differences between them. Canals’ transportation and decreased centering ratio were detected in both groups at all tested levels with insignificant smaller values in the M-D direction. Exception was found at 9mm level where a significantly highest transportation was found in R-S group (P= 0.022). Both instruments left untouched canal areas which were insignificantly greater in R-S group (26.5±8.93% for R40 and 31.7 ±4.96% for R-S). Conclusions: The tested systems caused small canal transportation with a comparatively better centering for Reciproc R40. Irrespective of the instrumentation kinematic, circumferential preparation of oval canals remains an inherent incapability. CBCT is a valuable tool allowing calculation of the canals’ volume.