Large Object table data file does not have expected size

I am a little bit confused by the following effect.
For test reasons I insert about 100000 large objects into the database. Each has
a size of 10240 Bytes (10K). So the expected size of the large object datafile
should be at least 1024000000 Bytes (about 976MB) just to hold the large objects.
But the according data file is much smaller than that. If I query the large
objetcs from psql all data seems to be there (i just randomly picked out some
large objects). I first thought there was a bug in my test program (not all
large objetcs are inserted), but I couldn't find one. Also this was unlikely,
since I always insert the same binary data (for the large objetc) in a simple loop.

Has anyone an idea why the datafiles are much smaller than I expect them to be?

Thanks, Andreas.

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