Six isomers of Yb@C-74 are considered, namely one cage with isolated pentagons, three isomers with a pentagon-pentagon junction, two structures with one pentagon-pentagon pair, and one heptagon. The computations based on the Gibbs energy point out the endohedral derived from the only C-74 cage with the isolated pentagons and from a cage with one pentagon-pentagon junction as the major and minor observed isomer, respectively. Temperatures giving the best agreement with the experimental production ratio are evaluated.