Even used motor oil and specifically clean motor oil is not a hazardous Chemical by DOT,EPA etc.
Solvents as defined by low flash points and flamability and dangerous vapors or corrosiveness are restricted by the airlines and airfreight services. FEDEX and UPS will handle some forms of Hazardous materials including highly corrosive and flamables but you must check with the carrier.
Motor oil used or new is NOT hazardous.
It is legal. I dont' have the regulations here, but they are interpreted differently by different airlines. Every couple of weeks I send from 30 to 80 samples (100 ml each) by DHL. I have to have sealable bottles, and a cardboard box. FedEx and UPS will not ship, as they use American Airlines from Bolivia to Miami.
I have quoted air shipment from the U.S. on pails, and it can be done, but is not cheap (3 pails for $750 freight). A freight forwarder can handle it.
I have to include the MSDS sheets.