Use of OIDS as primary keys

Hi!

I'm wondering how I can use the system generated OIDS
as primary keys. Does postgre automatically fill in
the system generated oid when a field of type oid is
created as the primary key? And if so, how do I read
it back on a record just created so I can use it as a
secondary key in another table? And lastly, is it even
a good idea to use the oid as keys at all when I'm
going to eventually migrate the data from one machine
to another?

Any help would be appreciated,
AJW

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