An expansion tool for use in a wellbore includes an expansion surface made up of a concave portion, a convex portion and a straight section therebetween. The straight section is formed according to a formula Y=(1.26) (X)−0.13, where X is the wall thickness of a tubular and Y is the length of the straight section. The concave portion and the convex portion have an arc length extending the concave portion to a trailing edge of the tool. The concave and convex portions are radius-shaped. The arrangement of the shapes and their relation to each other reduces relatively high and low contact pressures and lessens the effects of axial bending in a tubular or a connection.