The Refugio oil spill deposited 142,800 U.S. gallons (3,400 barrels) of crude oil onto an area in California considered one of the most biologically diverse coastlines of the west coast.

The Refugio oil spill occurred on May 19, 2015, on the Gaviota Coast in Santa Barbara County, California, United States. It contaminated one of the most biologically diverse areas of the West Coast of the United States with 142,800 U.S. gallons of crude oil. The corroded pipeline that caused the spill closed indefinitely, resulting in financial impacts to the county estimated as high as $74 million as it and a related pipeline remained out of service for three years. The cost of the cleanup was estimated by the company to be $96 million with overall expenses including expected legal claims and potential settlements to be around $257 million.

Petroleum, also known as crude oil or simply oil, is a naturally occurring, yellowish-black liquid chemical mixture found in geological formations, consisting mainly of hydrocarbons. The term petroleum refers both to naturally occurring unprocessed crude oil, as well as to petroleum products that consist of refined crude oil.

California is a state in the Western United States that lies on the Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares an international border with the Mexican state of Baja California to the south. With almost 40 million residents across an area of 163,696 square miles (423,970 km²), it is the largest state by population and third-largest by area.

The West Coast of the United States, also known as the Pacific Coast and the Western Seaboard, is the coastline along which the Western United States meets the North Pacific Ocean. The term typically refers to the contiguous U.S. states of California, Oregon, and Washington, but it occasionally includes Alaska and Hawaii in bureaucratic usage. For example, the U.S. Census Bureau considers both states to be part of a larger U.S. geographic division.