It was found that very many isolable or extractable metallofullerenes employ kinetically unstable isomers of C-78, C-80, and C-82 as carbon cages. These fullerene isomers are supposed to be stabilized by accepting one or more electrons from the encapsulated metal atoms. It seems that nature prefers to generate metallofullerenes with chemically reactive fullerene isomers. Some kinetically stable isomers Of C84 likewise form isolable metallofullerenes. All stability considerations were made using a bond resonance energy (BRE) model.