Photochemical oxidation (photo-oxidation) of crude oil spilled at sea has been studied for over half a century. However, prior to the 2010 Deepwater Horizon (DWH) oil spill, photo-oxidation was widely considered a secondary weathering process that impacted a small fraction of spilled oil. Accordingly, photo-oxidation was not included in oil spill fate and trajectory models and response operations. In this talk, I’ll describe several key findings related to the rates, pathways, controls, and impacts of crude oil photo-oxidation in the aftermath of the DWH spill. These findings have collectively changed the perspective of photochemical weathering in the oil spill sciences, leading to its inclusion in oil spill models and increased consideration during response operations. I’ll also share my perspective on the many reasons why it took a devastating environmental disaster to make such progress. Finally, I’ll discuss the role sunlight may play during future oil spills, including spills in colder, high-latitude waters where risks are increasing as a consequence of global climate change.