Left: dependence of the geodesic ISCO radius r_ISCO = r_ms on the NS angular momentum j and the oblateness factor . The shaded area indicates the Kerr-like region where r_ISCO decreases with increasing j. We note that for the concrete NS models we assume here, a fixed value of corresponds to a fixed NS central density ρ. Moreover, in the limit of the NS spacetime approaches the Kerr spacetime and values of correspond to the highest possible values of ρ (the oblateness parameter is also called the Kerr parameter). Right: dependence of compactness K on the NS spin frequency ν_spin and mass M. The shaded area indicates the region of K < 1 where the ISCO does not appear above the NS surface.