Since oil is a lipid, it does not freeze in the typical way freezing usually occurs, according to scientists at the University of Illinois. Lipids do not freeze, but the molecular movement slows down at colder temperatures.
Many lipids have a somewhat low melting temperature and some lipids are in liquid form even at room temperature. These lipids, including oils, are able to stay nearly in the same form no matter the temperature. Unlike water, lipids do not have a specific freezing point or melting point. The movement of the lipid's molecules will slow or stop depending on the decrease in temperature. Lipids will often become more solid when they are left in cold temperatures for long periods of time. This is not a true change in the structure of the lipids, but the chains of molecules simply have slower movements which allow the appearance of a solid.
Although lipids will not truly freeze, it does not take a lot of heat for them to get back to their original consistency. Lipids that have reached a somewhat solid form in colder temperatures can usually turn back into their liquid form after only a short amount of time in a normal room temperature atmosphere. There are some exceptions to the rules such as coconut oil, which is a solid at room temperature; and butter which turns into a solid more quickly in colder temperatures than other lipids.