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 g g 1, ks is 0.7 mg l 1, 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.