  We address the problem of resumming leading clustering logs in QCD jet
observables defined using the k_t, CA and SISCone algorithms. We specifically
choose the jet mass distribution as an example and calculate up to
order(alpha_s^4) clustering-log terms in the series expansion at single-log
accuracy. These terms are found to exhibit a pattern of exponentiation and we
are thus able to perform an all-orders analytical resummation for the
clustering logs. We also numerically calculate the non-global logs at large
N_c. We show that our result for the resummation of clustering logs is a very
good analytical approximation to the numerical result obtained using a
specialised Monte Carlo program.
