There are two varieties of barium meal: single and double contrast meals.

A single contrast meal uses only barium, a radioopaque (or positive) contrast medium, to image the upper gastrointestinal tract.

A double contrast meal uses barium as well as a radiolucent (or negative) contrast medium such as air, nitrogen, or carbon dioxide.

The double contrast meal is more useful as a diagnostic test, demonstrating mucosal details and allowing the detection of small mucosal lesions such as diverticula or polyps.