Using strain NCTC 11168 in carbon (serine)-limited continuous cultures we report the first detailed examination of oxygen-dependent changes in gene and protein expression in Campylobacter jejuni under conditions where the growth rate is fixed. We show that in steady-states established at μ = 0.2 h-1 over a wide-range of oxygen inputs, a perceived aerobiosis scale can be calibrated by the acetate excretion flux, which becomes zero when metabolism is fully aerobic (100% aerobiosis = 5% v/v oxygen in the gas inflow). A label-free proteomic analysis compared protein abundance (reported as the emPAI ratio) at 40% aerobiosis (= 1.88% v/v oxygen in the gas inflow) and 150% aerobiosis (= 7.5% v/v oxygen in the gas inflow) aerobiosis. This identified 857 proteins. Of 223 proteins more abundant at 40% aerobiosis, those involved in host colonisation and alternative pathways of electron transport were prominent. At 150% aerobiosis, 129 proteins were more abundant, including those involved in oxidative stress protection, citric-acid cycle, lactate and proline oxidation.