Max OID

I have a table that is used to control documents:
recno | integer | not null default
nextval('document_recno_seq'::regclass)
foreigntablename | character varying(255) | not null
foreignrecno | integer | not null
docforeigntablename | character varying(255) | not null
docforeignrecno | integer | not null
docforeigntext | character varying(255) | not null
documenttyperecno | integer | not null
version | character varying(20) | not null
loadeddate | date | not null
loadedtime | time without time zone | not null
usersrecno | integer | not null
title | character varying(40) | not null
description | character varying(255) |
doculookupcodesrecno | integer | not null
document | oid | not null
suffix | character varying(255) |

Each document is loaded using the large object commands and the OID of
the load then inserted as a ref number on the document table.
This has been working fine, but I had a major crash on the server and it
had to be rebuilt.
The database had been exported (pg_dump) - so I reimported (pg_restore)
the database.
If I now look at the oid (ie document.document) of the blob on the
numbers are in the range:
3159553408
3159553409
3159553410
3159553411
3159553412
3159553413
3159553414
3159553415
these numbers are above the field I use for the OID in the code (ie an
Integer - catering for 2 billion) - so the program no longer finds the
document to export.
Any ideas as to why did these OID's become so large after reimporting (I
am assuming here that they must have been under 2 billion before or else
the process could not have worked before)? And what limit is ther then
on this OID?