Estimates of BH mass M_BH in M101 ULX-1. The blue line represents M_BH versus the inclination angle i estimated using the dynamical method for HST data (taken from Liu et al. 2013), while the red line corresponds to our BH mass estimates based on X-ray data using the scaling technique (see Table 6). These two different methods give similar BH mass values with an assumption of small inclination angles.