Intravenous fat emulsions (IVFEs) provide essential fatty acids (EFAs) and are a dense source of energy in parenteral nutrition (PN). Parenterally administered lipid was introduced in the 17th century but plagued with side effects. The formulation of IVFEs later on made it a relatively safe component for administration to patients. Many ingredients are common to all IVFEs, yet the oil source(s) and its (their) percentage(s) makes them different from each other. The oil used dictates how IVFEs are metabolized and cleared from the body. The fatty acids (FAs) present in each type of oil provide unique beneficial and detrimental properties. This review provides an overview of IVFEs and discusses factors that would help clinicians choose the optimal product for their patients.