An expression list can contain up to 1000 expressions.
In addition to this, there might be other limitations to be respected, e.g. SQL*PLUS has documented limits like "command-line length" (=2500 characters) and "number of lines per SQL command" (=500 (assuming 80 characters per line)).
If you are adding so many values to your IN that the limit concerns you, maybe you should be considering a different approach anyway? Like perhaps storing the values in a global temporary table which you then join to the query.
I am calling a pl/sql function in powerbuilder to get this list and passing it back to a powerbuilder event. Im not sure the powerbuilder session will be able to see the values created in the table by the pl/sql function as it will be a different session.
There will probably be from 1 - 80 values in the IN. Is 80 an acceptable number of values for an IN?
Well it isn't as high as I feared it might be. Hopefully you will be using bind variables? Even with bind variables, there will still be up to 80 variants of the SQL statement parsed, but that's better than one per execution if the query is used a lot.