Abstract: Thin film thermal oxidative engine oil or other oleaginous liquid deposit device has an oleaginous test liquid placement volume; a heatable depositor surface in liquid communication with the volume; a supply for at least one of an oxidant and another substance which can adversely affect the test liquid; and a relatively thin film forming unit which delivers the test liquid to the depositor surface in a relatively thin film. Thin film thermal oxidative engine oil or other oleaginous fluid deposit method is also provided, which includes providing an oleaginous test liquid in an oleaginous test liquid placement volume; providing a depositor surface and heating said surface; delivering the test liquid as a relatively thin film to the heated depositor surface; providing to the test liquid an oxidizing and/or other substance which can adversely affect the test liquid; and observing any deposits or other activity thereabout. The invention is useful in oil testing.