out of memory error

We have a process that we successfully ran on virtually identical
databases.  The process completed fine on a machine with 8 gig of
memory.  The process fails when run on another machine that has 16 gig
of memory with the following error:

out of memory for query result

How is this possible?

The databases are almost identical.  By that I mean, the database that
the process completed properly is a dump of the database from the
machine where it failed.  There is about a week's more data in the
database where the process failed.  The whole database only takes up
about 13 gig of disk space.

Any clues would be appreciated.

--
Until later, Geoffrey

"I predict future happiness for America if they can prevent
the government from wasting the labors of the people under
the pretense of taking care of them."
- Thomas Jefferson