We considered the mechanism of the formation of the X-ray emission for massive stars. The X-ray spectra of 25 O stars were extracted from the archive of XMM-Newton data obtained in 2000–2014. We determined the distribution of the ratio of half-width at half-maximum to the wind terminal velocity for strong isolated spectral lines in the spectra of single, binary or multiple, and Of?p stars. Obtained distributions are similar for different types of objects. We established that the maximum of the ratio of half-width at half-maximum to the terminal wind velocity belongs to the interval 5–15%. In 2007, Pollock proposed this ratio for the X-ray emission of O stars to be ∼50% (so-called Pollock's paradigm). Our results show that the Pollock's paradigm is not correct.