The M(R) relationship for hybrid stars involving quark matter obeying the phenomenological equation of state (3) with ﹩a_{2}=( 180\ \mathrm{MeV}\,) ^{2}﹩. In each case the bag constant was chosen to give the desired transition density. The line with filled circles is the M(R) relation for a pure nuclear APR star. All the phases are neutral and homogeneous. We see that the maximum mass M_max is very sensitive to the QCD correction c but not to the transition density. For ﹩c=0.3﹩, which is close to the value suggested by Fraga et al. (2001), ﹩M_{\mathrm{max}\,}\approx 1.9\ M_{\odot }﹩. Note also that the ﹩c=0.3﹩ equation of state is so similar to APR that its M(R) curve is almost identical to that of pure APR.