This pivotal trial of the Obalon Balloon System is intended to generate safety and effectiveness data required to support a future marketing application. The trial has been designed to evaluate a 6-month use of the Obalon Balloon System as an adjunct to a nutrition and lifestyle behavior modification program.

Weight loss will be evaluated after the 6-month course to determine if a specific predefined superiority margin can be achieved in the device group compared to a sham-control group.

Inclusion Criteria:

1. Male or female between the ages of 22-64 years
2. Current BMI of 30.0 - 40 kg/m2
3. Previously attempted to lose weight unsuccessfully using a medically supervised or non-medically supervised diet
4. Willing to attend all protocol-specified follow-up visits plus any additional follow-up visits as required throughout the entire study period
5. Willing to avoid non-commercial air travel and scuba diving during the entire study period
6. Willing to avoid medications or other substances known to effect weight changes during the study
7. Willing to avoid Non-Steroidal Anti-inflammatory Drugs (NSAIDs) or other medications known to be gastric irritants during the study
8. Willing to use contraception and avoid pregnancy during the study if the subject is female with child bearing potential
9. Willing to provide written informed consent

Exclusion Criteria:

1. Significant weight loss in the past 12 months
2. Use of medications or other substances known to induce weight gain or weight loss
3. Participation in any clinical study at the start of this trial or in the last year
4. Known history of endocrine disorders affecting weight
5. Currently receiving chronic steroid or immunosuppressive therapy or has previously been diagnosed with HIV
6. Subjects diagnosed with bulimia, binge eating, compulsive overeating, high liquid calorie intake habits or similar eating related psychological disorders
7. Intent to undergo gastric surgery or gastric banding during the study period or within the 6 month period after completion of this study
8. Prior use of any weight loss medical device
9. Known history of structural or functional disorders of the esophagus
10. Known history of structural or functional disorder of the esophagus, including any swallowing disorder, esophageal chest pain disorders, or drug refractory esophageal reflux symptoms
11. Known history of structural or functional disorders of the stomach
12. Known history of a structural or functional disorder of the stomach, including any symptoms of chronic upper abdominal pain, chronic nausea, chronic vomiting, chronic dyspepsia or symptoms suggestive of gastroparesis, including post-prandial fullness or pain, post-prandial nausea or vomiting or early satiety
13. Known history of duodenal ulcer, intestinal diverticula (diverticulitis), intestinal varices, intestinal stricture/stenosis, small bowel obstruction, or any other obstructive disorder of the gastrointestinal (GI) tract
14. Currently have ongoing symptoms suggestive of intermittent small bowel obstruction, such as recurrent bouts of post-prandial abdominal pain, nausea or vomiting
15. Known history irritable bowel syndrome, radiation enteritis or other inflammatory bowel disease, such as Crohn's disease
16. Known history of GI surgeries that may have resulted in anatomical GI tract abnormalities
17. Type 1 diabetes
18. Type 2 diabetes requiring insulin or other hypoglycemic oral agents.
19. Experienced a myocardial infarction, has a known history of angina, a known history of congestive heart failure, or is currently being medically treated for any other cardiac condition
20. Poorly controlled hypertension, (≥ 160 mmHg Systolic and ≥ 100mmHg Diastolic).
21. End stage renal disease or requiring hemodialysis within the past 6 months
22. Unwilling or unable to avoid Non-Steroidal Anti-Inflammatory Drugs (NSAIDs), including Aspirin, Diclofenac, Ibuprofen, Naproxen, or other medications known to be gastric irritants beginning two weeks prior to enrollment and throughout the entire study period
23. Subjects taking medications on specified hourly intervals that may be affected by changes to gastric emptying
24. Subjects requiring the use of anti-platelet drugs or other agents affecting the normal clotting of blood
25. Untreated or unstable alcohol or illicit drug addiction
26. Known history of allergies to any component of the device materials
27. Currently pregnant or breastfeeding or intention of becoming pregnant during the study
28. Life expectancy less than 1 year or severe renal, hepatic, pulmonary or other medical condition, in the opinion of the investigator
29. Subject is employed by the investigator, or is a close relative of the investigator, or the investigator's staff
30. Subject is a close relative of another subject already enrolled in the study.
31. Any other condition that, in the opinion of the investigator, would interfere with subject participation, may confound the study results, or interfere with compliance with the study (e.g., psychosocial issues).