Objective: The extent to which different types of breakfasts affect appetite and food intake is unclear. To assess the satiety effects of a high-fiber cereal, we compared oatmeal, isocaloric corn flakes, and water. Subjects/Methods: Thirty-six subjects (18 lean, 18 overweight) were assigned to three conditions in a randomized sequence on different days. Ratings of hunger and fullness were obtained concurrently with blood samples for measuring concentrations of glucose, insulin, glucagon, leptin, and acetaminophen (gastric emptying tracer). Appetite was assessed by calculating the area under the curve (AUC) for fullness and hunger, and by measuring food intake of an ad libitum lunch meal at 180 min. Results: Lunch meal intake was lowest after consuming oatmeal (p < 0.00001), which was lower for overweight subjects than lean subjects (p = 0.007). Fullness AUC was greatest (p = 0.00001), and hunger AUC lowest (p < 0.001) after consuming oatmeal. At 180 min, blood glucose was lowest after the corn flakes (p = 0.0001). Insulin AUC was greater for both cereals than water (p < 0.00001). Leptin AUC and glucagon AUC values did not differ between conditions. Acetaminophen concentrations peaked latest after consuming oatmeal (p = 0.046), reflecting slower gastric emptying. Conclusions: Satiety was greater and ad libitum test meal intake lower after consuming oatmeal than after corn flakes, especially in the overweight subjects.