A measurement of triple gauge boson couplings is presented, based on W-pair data recorded by the OPAL detector at LEP during 1998 at a centre-of-mass energy of 189 GeV with an integrated luminosity of 183 pb −1−1 . After combining with our previous measurements at centre-of-mass energies of 161–183 GeV we obtain κ=0.97+0.20−0.16, gz1=0.991+0.060−0.057 and λ=−0.110+0.058−0.055, where the errors include both statistical and systematic uncertainties and each coupling is determined by setting the other two couplings to their Standard Model values. These results are consistent with the Standard Model expectations.