The AS number space uses a 16-bit field. There are 65,536 unique as numbers, of which 64,510 are useable. At present some 38,910 AS numbers have been passed into the RIR system, leaving 25,600 in the unallocated pool. This presentation explores a number of techniques of trend analysis to derive a predictive model of AS number consumption to derive an estimate of AS number exhaustion. The presentation looks at the 4-byte AS number proposal and the associated transition plan, and makes some recommendations as to a schedule for a transition from the 2-byte to a 4-byte AS number.