Much of the oil spilled into the Kuwait desert during the conflict of 1991 still survives as “oil lakes.” Oil spills are usually rapidly degraded by a combination of biodegradation, water washing, evaporation, and oxidation, but because of the low rainfall and lack of near_surface water in the Kuwaiti desert, the first two of these processes cannot operate. Evaporation appears to be the dominant degradation mechanism. We have simulated evaporation of a Kuwait crude oil (from Burgan field) and a Venezuelan crude oil at temperatures of 25, 30, 40, and 50°C and at various air flow rates from 25 to 100 mL/min. Weight loss is initially rapid but subsequently decreases through time. After 30% weight loss the API gravity of the Burgan crude decreased to 22° from an initial value of 30°, and viscosity increased from 65.3 to 300.5 centipoise. Evaporative reduction of oil lake volume and reduced surface area lead to shoreline movement. Applying a cone-shaped model that relates volume loss to distance moved by the shoreline showed that the retreat is much smaller than predicted, implying that the lakes have lost considerably less volume by evaporation than expected. It seems likely that a devolatilized, high-viscosity, high-density, near-surface layer develops, protecting the underlying oil and decreasing the overall rate of evaporation.