The aim of this study is to establish and calculate the exact allometric relationship between the total metabolic energy per life span and the body mass in a wide range of mammals with about six orders of magnitude variation of the body mass of animals. The study shows that it exists a linear relationship between the total metabolic energy per life span PT(ls) (kJ) and the body mass M (kg) of 95 mammals (3 monotremes, Subclass Prototheria, 16 marsupialis (Subclass Theria, Infraclass Metatheria) and 76 placentals (Subclass Theria, Infraclass Eutheria)) from type: PT(ls)=A(ls)(+)M(1.0511), where P (kJ/day) is the basal rate of metabolism and T(ls) (days) is the mean life span of animals. The linear coefficient A(ls)(+)=7.158x10(5) kJ/kg is the total metabolic energy, exhausted during the life span per 1 kg body mass of the animals. The mean values of the total metabolic energy per life span, per unit body mass (A(ls)) for orders from Subclass Prototheria and Theria (Infraclass Metatheria) and orders Xenarthra, Pholidota, Soricomorpha, Rodentia (Infraclass Eutheria) varied negligible in interval (4.656-5.80)x10(5) kJ/kg. The coefficient A(ls) grows from (7.68-8.36)x10(5) kJ/kg in Lagomorpha and Artiodactyla (Eutheria) to (10.58-12.64)x10(5) kJ/kg in orders Carnivora, Pinnipeda and Chiroptera (Eutheria). A(ls) grows maximum to 18.5x10(5) kJ/kg in Primates. Thus, the values of coefficient A(ls) differ maximum four-fold in all orders. Across the all species the values of A(ls) are changes about one order of magnitude. Consequently, our survey shows that the changes of the body mass, basal metabolic rate and the life span of animals are three mutually related parameters, so that the product A(ls)=(PT(ls))/M remains relatively constant in comparison to 1 million fold difference in body mass and total metabolic energy per life span between mammals.