We obtain a criterion for determining the stability of singular limit cycles of Abel equations x' = A(t)x(3) + B(t)x(2). This stability controls the possible saddle-node bifurcations of limit cycles. Therefore, studying the Hopf-like bifurcations at x = 0, together with the bifurcations at infinity of a suitable compactification of the equations, we obtain upper bounds of their number of limit cycles. As an illustration of this approach, we prove that the family x(') = at(t - t(A))x(3) + b(t - t(B))x(2), with a,b>0, has at most two positive limit cycles for any t(B), t(A).
