Gas and bloating can have many causes, including:

• Bowel obstruction. Symptoms may include abdominal pain, nausea, vomiting, gas, and bloating.
• Cirrhosis of the liver. Symptoms may include a poor appetite, nausea, diarrhea or constipation, a bloated (distended) abdomen, and dull abdominal discomfort.
• Colon or rectal cancer. Symptoms may include diarrhea or constipation, narrow stools, abdominal pain, bloating, gas, weight loss, and decreased appetite.
• Crohn's disease. Symptoms may include lower abdominal cramping, diarrhea, weight loss, fever, and bleeding from the rectum.
• Diabetes. People who have long-standing diabetes may develop bowel problems that cause bloating and gas.
• Diverticulitis. Symptoms may include abdominal cramping, diarrhea, bloating, and gas.
• Gallstones. Symptoms may include pain in the upper right side of the abdomen, chest, upper back, or right shoulder following a meal of high-fat foods. Additional symptoms include nausea, vomiting, fever, belching, gas, heartburn, or pale stools.
• Ovarian cancer. When symptoms are present they may be vague, such as weight gain, increased abdominal girth, gas, and bloating. Ovarian cancer frequently does not cause symptoms.
• Parasitic infections, such as giardiasis, worms, or amebiasis. Symptoms may include diarrhea, dehydration, mucus or blood in the stools, abdominal cramps, fatigue, weight loss, and gas.
• Peptic ulcer disease. Symptoms include a burning, aching, gnawing pain between the belly button and the breastbone that may extend to the back, loss of appetite, weight loss, bloating, gas, nausea, or vomiting.
• Splenic flexure syndrome. In this chronic condition, gas becomes trapped at the bends in the colon. Symptoms include bloating, muscle spasms, and upper abdominal pain.
• Ulcerative colitis. The most common symptoms are abdominal pain or cramping and diarrhea.

Gas also often occurs during the recovery phase of abdominal surgery. Gas-bloat syndrome may occur after surgery to correct gastroesophageal reflux disease (GERD).