Predictions of the effect of clumping on the wind properties of O-type stars L. E. Muijres, A. de Koter, J. S. Vink, J. Krtička, J. Kubát and N. Langer A&A, 526 (2011) A32 Published online: 17 December 2010 DOI: 10.1051/0004-6361/201014290