I have a Web Service (in java) on a Oracle WebLogic 10.3 that does all kinds of database queries. Recently I started stress tests. It passed the repetition tests (invoke the WS several 1000 times serially) but problems become to arise when concurrency testing began. Making as much as 2 concurrent calls results in errors. When doing proper tests the results looked like the WS wasn't able to handle concurrent calls at all, which obviously should not be the case. Errors included null pointer exceptions, closed connections or prepared statements, etc. I am bit stumped at this, specially since I was unable to find any kind of configuration options that could effect this, but then again my knowledge of the WLS is quite limited.