We present measurements of the transport spin polarization of NixFe1-x (0 less than or equal to x less than or equal to 1) using the recently developed point-contact Andreev reflection technique, and compare them with our first-principles calculations of the spin polarization for this system. Surprisingly, the measured spin polarization is almost composition independent. The results clearly demonstrate that the sign of the transport spin polarization does not coincide with that of the difference of the densities of states at the Fermi level. Calculations indicate that the independence of the spin polarization of the composition is due to compensation of density of states and Fermi velocity in the s and d bands.