Kernels Used in Fedora Core

FC1: 2.4.19
FC2: 2.6
FC3: 2.6
FC4: 2.6.11
FC5: 2.6.16
FC6: 2.6.18
FC7: 2.6.21
FC8: Coming (8. November 2007)

Reference:
Fedora (Linux distribution) - Wikipedia