Vapor intrusion is associated with subsurface sources of both chlorinated VOCs and petroleum VOCs; however, petroleum vapor intrusion has been reported to occur under a narrower range of hydrogeologic settings. Research conducted over the last several years including field studies, evaluation of large datasets, and modeling studies, has provided an improved understanding of the differences in vapor intrusion associated with chlorinated VOCs and petroleum VOCs. When oxygen is present in the vadose zone, aerobic biodegradation typically results in rapid attenuation of petroleum VOCs diffusing upwards from deeper sources. At many building sites, wind-driven advection and/or building pressure fluctuations provide sufficient oxygen transport below the foundation to support this aerobic biodegradation. In such cases, there is limited potential for vapor intrusion from dissolved sources of petroleum VOCs unless preferential migration pathways are present. These findings support a framework for the evaluation of vapor intrusion at petroleum hydrocarbon sites that involves simple screening for preferential pathways at sites with sufficient vertical separation between the building and a dissolved source (e.g., 3 m) or a LNAPL source (e.g., 10 m), but a more intensive investigation at sites with petroleum sources in closer proximity to the building.