What condiment is the base of Alabama white barbecue sauce?

The base condiment of Alabama white barbecue sauce is mayonnaise.

Alabama white sauce is a mayonnaise-based barbecue sauce, usually thinned and sharpened with vinegar or lemon juice. Recipes commonly add salt, black pepper, cayenne, and horseradish, producing a creamy, tangy sauce rather than the darker, sweeter tomato-based sauces associated with many other American barbecue regions.

The sauce is strongly associated with barbecue chicken, although it can also accompany pork, turkey, vegetables, and other grilled foods. It is often brushed on near the end of cooking or served as a dipping sauce, since the mayonnaise base is not treated like a long-simmered tomato sauce.

The style is commonly credited to Bob Gibson of Big Bob Gibson Bar-B-Q in Decatur, Alabama, where it is believed to have been created in 1925. Alabama also has vinegar-based and tomato-based barbecue sauces, so “Alabama sauce” does not always mean white sauce. The question’s wording specifically identifies the white variety.