Pseudomonas methylotrophus is used to produce single cell protein from methanol in a 1000-m3 pressure-cycle airlift fermenter. The biomass yield from substrate is 0.41 gg1, K, is 0.7 mg L1, and the maximum specific growth rate is 0.44 h-1. The medium contains 4% (w/v) methanol. A substrate conversion of 98% is desirable. The reactor may be operated in either batch or continuous mode. If operated in batch, an inoculum of 0.01% (w/v) is used and the downtime between batches is 20 h. If continuous operations are used at steady state, a downtime of 25 days is expected per year. Neglecting maintenance requirements, compare the annual biomass production achieved using batch and continuous reactors.