[en] When performing calculations on boiling water reactors it is necessary to establish a relation between the average velocity of the steam, V_g, and that of the water, V_f, in the fuel channels. This is usually done through establishing an expression for the slip ratio S=V_g/V_f. In the literature a number of such slip correlations - all based on measurements - has been presented. A comparison between some of these correlations has been performed in this paper. While the correlations have some general trends in common, the numerical values of S obtained with the correlations may vary significantly. Further, in spite of the fact that various flow regimes into account. This raises the question: How reliable is the use of slip correlations? (au)