the System.Data.OracleClient does not support arrays.
Depending on your need, you will either need to implement this via nested table types (via UDTs or assoc. arrays) using the ODP.net clients. This is probably a good direction to go, esp. since .net 4.0 has deprecated System.Data.OracleClient.
But if you are stuck with the System.Data.OracleClient and you are really just trying to do a variable in-list, you can do this by passing in a string and following some of these suggestions:
hope this helps