This paper describes natural garlic oil (NGO) as a highperformance, environmentally friendly, extreme pressure additive for lubricating oils. The chemical composition of NGO was analyzed by gas chromatography−mass spectrometry (GC-MS). The load-carrying capacities of NGO and sulfurized isobutylene (SIB) in different base fluids were comparatively evaluated by a four-ball tester and an optimol SRV-IV oscillating reciprocating friction and wear tester (SRV tester). The four-ball test results revealed that incorporation of 1 wt % NGO into the base fluids could significantly improve the weld point of the base fluids from approximately 126 to 800 kgf or higher. Moreover, the four-ball test and SRV test results demonstrated that NGO could provide superior load-carrying ability in the selected base fluids than the conventional extreme pressure additive SIB. In addition, X-ray photoelectron spectroscopy (XPS) results showed that NGO and SIB experienced a similar tribochemical process with the generation of tribofilms composed with iron oxides, iron sulfates, iron sulfide, etc. NGO showed great promise for use as an effective, eco-friendly, extreme pressure additive for application in environmentally sensitive areas.