Linux Setup question

Hi,
        I've got the following problem:

      I've installed Slackware 2.0.0 on a P133 with 16 Mb of RAM, and I've configured a 48Mb of swap. But when I run an "/usr/bin/awk" to change the order of two columns, over a big
file ( 7697892 bytes), my swap become smaller and smaller, until my machine has not more free swap and then return a memory error.
      When I begin the process there are 48 Mb of free swap.

      Some lines of the file are:

[...]
1567 kkkkkkkkkk 78
3910 oooooooooo 92
7930 llllllllll 71
[...]

        I appreciate all the help I can get with this problem.

        Thanks in advance.