Oil solution for carbon fiber precursors and carbon fiber precursor

An oil agent for a carbon fiber precursor, comprising

• a base component,
• a cationic surfactant,
• a nonionic surfactant, and
• an optional organic polybasic acid salt,
• wherein the cationic surfactant is a compound represented by Chemical Formula 1:
• in Chemical Formula 1,
• wherein R1 is selected from the group consisting of an alkyl and an alkenyl group having 7 to 18 carbon atoms,
• wherein R2 is selected from the group consisting of a hydroxyethyl group, a hydroxypropyl group, and a propyl group,
• wherein R3 is selected from the group consisting of a methyl and an ethyl group, and
• wherein Y− is selected from the group consisting of a methylsulfate group, an ethylsulfate group, and an organic group represented by Chemical Formula 2:
• in Chemical Formula 2,
• wherein R4, R5 is selected from the group consisting of a methyl and an ethyl group, wherein the base component is an amino-modified silicone that is liquid at 25° C. and the oil agent comprises 50 to 95% by mass of the base component, 0.01 to 30% by mass of the cationic surfactant, 3 to 45% by mass of the nonionic surfactant and 15% by mass or less of the optional organic polybasic acid salt such that the total content of the base component, the cationic surfactant, the nonionic surfactant, and the optional polybasic acid salt is 100% by mass, and wherein the nonionic surfactant is a compound obtained by addition reaction of ethylene oxide and/or propylene oxide to an organic alcohol at a ratio of 1 to 50 mol ethylene oxide and/or propylene oxide with 1 mol of an organic alcohol having 4 to 40 carbon atoms.