Polycyclic aromatic hydrocarbons (PAHs) are a class of organic compounds found in the environment associated with natural and anthropogenic activities such as the refinement and use of petroleum hydrocarbons as fuels and lubricants. When an oil spill occurs in California, an understanding of pre-spill or ambient levels of PAHs is crucial for understanding the existing environmental conditions before a release occurs. Anthropogenic (e.g., vehicle and boat exhaust, wood burning, industrial activities, oil spills) and natural releases (i.e., forest fires, oil seeps) of PAHs are common sources of these compounds in the environment. Ambient or pre-spill data are critical to identify the need for, and scope of, subsequent environmental sampling, and injury assessment. The Office of Spill Prevention and Response (OSPR) in collaboration with industry representatives (Chevron) and other state and federal trustee agencies (Department of Fish and Game, U.S. Fish and Wildlife Service, Bureau of Land Management, National Oceanic and Atmospheric Administration) have collected environmental samples (e.g., water, sediment, and tissue) for polycyclic aromatic hydrocarbon (PAH) chemical analysis from coastal and inland locations. In addition, plans to collect PAH monitoring data in California for the purpose of being prepared for oil spills and assessing natural resource injuries have been developed. Between 2011 and 2019, Chevron and the Trustees collected samples in Eureka/Humboldt Bay, Richmond, El Segundo, and San Diego, CA for PAH analysis to begin assessing ambient conditions. Chevron and the Trustees have the common understanding that the interpretation of statistical comparisons of these data to spill data (in the event one occurs) must take into consideration the sample size and geographic coverage of the available PAH monitoring data. From 2017 to present, CDFW-OSPR has collected samples in the Feather River Canyon, along the Upper Sacramento River, in Elkhorn Slough and Monterey Bay.