This article links up the disastrous history of fossil fuels with the celebrated ecology of mangroves. Building on ethnographic and historical research in Puerto Rico and St. Croix, it outlines the often neglected but quite consequential place of crude oil in the Caribbean. Following the construction of what became the second largest refinery in the world, I describe how the imperial energy networks of the United States first came to the Caribbean. Troubling a popular origin story of the Caribbean, colonial and industry leaders voiced a robust critique of the plantation in order to justify the introduction of these enclave refineries. Imperial energy networks welcomed an unprecedented problem to the region: coastal oil spills. The scientific and legal response to these spills brought new attention to the vital relationality of mangroves. Rather perversely, the destruction of the mangroves in the Caribbean—in which crude oil played the leading role—opened mangroves up to new forms of knowledge and care. While many claim that fossil fuels helped cultivate a modern disregard for the natural world, I show how the negative ecologies of fossil fuels also instigated new scientific and political appreciations for the liveliness of the natural world. This story of oil in the Caribbean has implications for scholarly debates around the so-called Anthropocene. Against scholarship that looks at the coming disaster of crude oil as an epochal break in thought and politics, this paper instead describes the long history of acknowledging and managing the disastrous qualities of fossil fuels.