An oil-based ink composition for inkjet printers contains a fixing polymer and a solvent represented by the following formula (1): wherein X1 represents an alkyl group, X2 represents a hydrogen atom or alkyl group, and n stands for an integer of from 1 to 4. The fixing polymer is an acrylic polymer obtained by subjecting an acrylic monomer to solution polymerization with a radical polymerization initiator in the solvent. A production process of the oil-based ink composition is also disclosed.