A theoretical quantitative description is given for non-periodic oscil
lations observed in a current vs. gate voltage characteristics of cyli
ndrical quantum dots. Energy eigenvalues and chemical potentials for a
system of N confined electrons (N = 1,...,13) are calculated by the u
nrestricted Hartree-Fock method with a confinement potential proportio
nal to the gate voltage. The positions of the observed peaks of the cu
rrent are reproduced with a very good accuracy. The non-periodicity of
the characteristic is explained as a result of the shell filling, whi
ch is a signature of the quantum Coulomb blockade.