A method for determination of probability of electrical breakdown of gases ispresented in this paper and results are compared with theory. The method is based onthe measurements of breakdown time delay at different afterglow periods (relaxationtimes), where the secondary electron yield initiating breakdown is caused by residualactive states reMayning from the preceding glow. Measurements are carried out at lowpd (gas pressure times electrode spacing) of nitrogen and higher overvoltages up to2.1U s (U s: the static breakdown voltage). The experimentallydetermined breakdown probability is fitted by theoretical expressions for both theTownsend and streamer model of electrical breakdown, with particular attention to thehigher overvoltages. On the basis of our measurements and theoretical fit it can beconcluded that the Townsend mechanism is applicable at low pd value over the wholerange of overvoltage applied and a value of a secondary emission coefficient forgold-plated copper cathode is obtained. With the decrease of the breakdown probabilityand electron yield the distributions of delay times become broader and centered atlarger delay times, and the positive asymmetry and roundness increase.