The two most popular open source fortran compilers are g77 and gfortran. Unfortunately, they are not ABI compatible, which means that concretely you should avoid mixing libraries built with one with another.

You can check which fortran compiler was used by looking at the dependencies a library was build with:

ldd /usr/lib64/libblas.so

If there is a dependency

libgfortran.so.3 => ...

gfortran was used. If a dependency is

libg2c.so => ...

the g77 was used.