I came across a weird problem this morning. What would cause a file to be reported as 251M for used space and 1.3G for size on disk?

[root@cc1lnx5 axprac]# ls -sh cafrap_1.dbf; ls -lh cafrap_1.dbf
251M cafrap_1.dbf
-rw-r----- 1 oraxprac axprac 1.3G Apr 15 09:47 cafrap_1.dbf
[root@cc1lnx5 axprac]#


I have seen this to a smaller extent with some files but never a variance of this size.
This file happens to be an Oracle 11G database table file.