PURPOSE: To obtain a steel-made oil ring, with a coil expander, having high forming accuracy and a raw material application ratio with a few working processes by making a ring main body having a column part at the approximate middle part and projections protruded from both the end parts of the column part and providing both left and right side profile shapes of a symmetric continuous curve.

CONSTITUTION: A ring main body 1 has a column part 2 in the approximate middle part, and projections 3 and 3' having a width (b) projections 4 and 4' having a width (b') which are projected to the right side and the left side respectively from both the upper and lower end parts of the column part 2. A profile shape, formed with the column part 2 and the projections 3 and 3', is formed as a quadratic curve. Consequently the ring main body 1 has an approximate X-shaped cross section having a nearly symmetric shape in up and down and left and right. Moreover a chrome plating layer 7 having abrasion resistance is formed on the part of the projections 3 and 3' slidedly contacting a cylinder wall. Consequently the manufacture of a roll die is easy, forming is possible in a high forming accuracy condition, and the prolonging the life of the die is allowed.