This study compared the gap volume and sealer penetration in C‐shaped root canals prepared with adaptive core rotary files and obturated with cold hydraulic compaction using calcium‐silicate sealer, warm vertical hybrid compaction, or lateral compaction using epoxy‐resin sealer. Thirty‐six extracted mandibular molars with pulpal floor configuration Types I and III were used. The teeth were prepared using XP‐Shaper and XP‐Finisher and obturated with: group 1: cold hydraulic compaction/calcium silicate, group 2: warm vertical hybrid compaction/epoxy resin, or group 3: lateral compaction/epoxy resin. The gap volume was evaluated using μ‐CT. The sealer penetration depth and area were evaluated using confocal laser scanning microscopy. The gap volume in groups 1, 2, and 3 was 0.82%, 0.24%, 0.80%, respectively, which were not significantly different (p > 0.05). The gap volumes in the obturated C‐shaped canals were not significantly different among the CHC/CSBS, WHC/ERS, or LC/ERS groups. CHC/CSBS was the most convenient technique.