Black hole masses of EXO 1846−031 obtained from X-ray observations. The black straight lines represent the black hole masses estimated using the R_ISCO derived from diskbb model fittings with NICER spectra, assuming the inclination range of 40° −74° and a non-spinning black hole. The dark grey region shows the mass range additionally satisfying the empirical condition of index transition luminosity estimated from the Swift/XRT spectrum. Each solid black curve in the bottom region indicates the constraint on black hole mass for different Eddington ratios (0.76%, 1.44%, and 2.75%) of the transition luminosity L_tran. The 90% confidence ranges are shown with accompanying dashed black curves. The solid curve marked with L_peak/L_Edd = 8% indicates the upper limit of mass estimated assuming the peak luminosity occurs at 8%L_Edd and a high inclination of 74°. The colored straight lines represent the masses estimated using the R_ISCO and spin obtained from the diskbb+reflection models for X2, X3 and X4 observations. Their corresponding 90% confidence ranges are shown with accompanying dashed lines in the same colors. The red star mark the black hole masses suggested by the kerrbb+relxillNS model (a = 0.998) for X3. For reference, the masses suggested by the kerrbb+relxillNS+gauss model (a = 0.998) for X3 and X4 are shown with colored diamonds.