The file format convention for ILOG CPLEX SOS files uses set declaration lines and member declaration lines, both of which begin in column 2 or beyond.

In a set declaration line, columns 2 and 3 specify S1 or S2, and column 5 or beyond sets priority.

In a member declaration line, column 5 or beyond specifies a variable name, followed by one or more spaces, followed by the reference row value.

In the following example, the SOS file specifies that variables x1, x2, x4, and x5 are members of a special ordered set of Type 1, and that the weights for these SOS variables are to be 10000, 20000, 40000, and 50000, respectively. The branching priority for the set as a whole is 10; that priority are compared with the priority assigned to other integer variables in the model.

NAME
 S1                   10
    x1                  10000
    x2                  20000
    x4                  40000
    x5                  50000
ENDATA