Except for the presence of saturated and unsaturated hydrocarbon groups, fat and oil have almost identical chemical structures. Saturated indicates there will be carbon-carbon single bonds, and the bonds will be stronger sigma bonds. That's why saturated groups are solid at room temperature, and fat is one of them. Unsaturated groups, on the other hand, have molecules that are liquid at room temperature and are known as oil. The primary distinction is between the saturated and unsaturated hydrocarbon groups.