  The energy evolution of average multiplicities of quark and gluon jets is
studied in perturbative QCD. Higher order (3NLO) terms in the perturbative
expansion of equations for the generating functions are found. First and second
derivatives of average multiplicities are calculated. The mean multiplicity of
gluon jets is larger than that of quark jets and evolves more rapidly with
energy. It is shown which quantities are most sensitive to higher order
perturbative and nonperturbative corrections. We define the energy regions
where the corrections to different quantities are important. The latest
experimental data are discussed.
