What causes distended stomach and upper abdominal area?

The most common cause of upper abdominal distention is retained gas within the stomach or intestines. Eating excessive gas forming foods, lactose or other food intolerance, irritable bowel syndrome, decreased stomach or bowel motility, or an intestinal obstruction could be the underlying problem. Fluid accumulation in the area between the abdominal organs, known as ascites, would usually cause distention throughout the belly, not just in the upper part of the abdomen.