Ink composition for oil-based ballpoint pen and method for production thereof, and ballpoint pen refill

A method for producing an ink composition for an oil-based ballpoint pen comprising:

• formulating and mixing an oil-soluble dye, water, an organic solvent whose vapor pressure at 20° C. is 0.5 mmHg or more and which dissolves the water, and an organic solvent whose vapor pressure at 20° C. is 0.1 mmHg or less and which dissolves the organic solvent whose vapor pressure at 20° C. is 0.5 mmHg or more at a given ratio where each is not 0, wherein the predetermined ratio is within the range where a total of the water, the organic solvent whose vapor pressure at 20° C. is 0.5 mmHg or more and which dissolves the water, and the organic solvent whose vapor pressure at 20° C. is 0.1 mmHg or less and which dissolves the organic solvent whose vapor pressure at 20° C. is 0.5 mmHg or more is 20 to 75% by mass and the water is 2.0 to 15.0% by mass, and the ink composition contains the organic solvent whose vapor pressure at 20° C. is 0.5 mmHg or more is 3.0 to 30.0% by mass based on the entire mass of the ink composition.