A novel approach to controlling deep ocean oil spills, pioneered in the 2010 Deepwater Horizon disaster, is now being challenged as ineffective. During the spill, emergency responders injected more than 2 million liters of toxic oil dispersants directly into the plume of hot oil billowing from near the sea floor. Proponents say the strategy helped dissipate the oil before it reached the surface, reducing damage to coastal shorelines. But new research suggests the dispersant might have made little difference. The heated debate comes as governments and the energy industry are preparing to use deep-sea dispersants again if a similar disaster happens.