Let H x a regular Hausdorff method and P(w)=∑ ak wk a power series with positive radius of convergence. A theorem of Okada states that P(w) is summable (H x ) for w in a certain starshaped region G(H x ,P). We call G=G(H x ,P) the exact region of summability for P if summability cannot hold for any w\( \in \bar G\) Okada's theorem is said to be sharp for Hx if G(Hx,P) is the exact region of summability for any P.