Fortran does not have a standard ABI like C does. Factor supports the following Fortran ABIs:

•	gfortran-abi is used by gfortran, the Fortran compiler included with GCC 4.
•	f2c-abi is used by the F2C Fortran-to-C translator and G77, the Fortran compiler included with GCC 3.x and earlier. It is also used by gfortran when compiling with the -ff2c flag.
•	intel-unix-abi is used by the Intel Fortran Compiler on Linux and macOS.
•	intel-windows-abi is used by the Intel Fortran Compiler on Windows.

A library's ABI is specified when that library is opened by the add-fortran-library word.