Single W boson production in electron-positron collisions is studied with the L3 detector at LEP. The data sample collected at a centre-of-mass energy of √s=188.7 GeV corresponds to an integrated luminosity of 176.4 pb-1. Events with a single energetic lepton or two acoplanar hadronic jets are selected. Within phase-space cuts, the total cross-section is measured to be 053±0.12±0.03 pb, consistent with the Standard Model expectation. Including our single W boson results obtained at lower √s, the WWγ gauge couplings κγ and λγ are determined to be κγ=0.93±0.16±0.09 and λγ=−0.31+0.68−0.19±0.13.