A common area is a data-only section that can be shared by multiple sections within the module. Common areas can have a name, and if unnamed a name consisting of a single blank will be assumed. The only supported text class for common areas is B_TEXT. If no identically-named CSECT is present, the storage allocated to the COMMON is determined by the longest COMMON definition.

Common areas provide shared space in the module text for data, not instructions. Common areas cannot have initial data values; however, if both a section (CSECT) and common area of the same name are present in the module, the CSECT will initialize the COMMON area. Note that such a CSECT must be at least as long as the longest COMMON definition.

Common areas are normally located at the end (highest virtual address) of the module, but can be relocated by specifying the common area name in the ORDER control statement. When creating a module in overlay format, if a common area is referenced by sections in different paths then it will be moved to a segment higher in the structure (closer to the root segment) that is common to both paths.