The cross-section for the process e(+)e(-) --> W+ W- has been measured with the data sample collected by DELPHI at an average centre-of-mass energy of 189 GeV and corresponding to an integrated luminosity of 155 pb(-1). Based on the 2392 events selected as WW candidates, the cross-section for the doubly resonant process e(+)e(-) --> W+W- has been measured to be 15.83 +/- 0.38 (stat) +/- 0.20(syst)pb. The branching fractions of the W decay were also measured and found to be in good agreement with the Standard Model expectation. From these a value of the CKM mixing matrix element \ V-cs\ = 1.001 +/- 0.040 (stat) +/- 0.020(syst) was derived. (C) 2000 Elsevier Science B.V. All rights reserved.
