As ANSYS staff we can't answer too specifically on a public forum: the wider community can.
Re surface tension, read up on the subject: different materials have different surface tension values. You also need to work out what sort of oil you're using as "oil" covers anything from olive oil to Saudi Heavy bitumen!
Have you read up on the VOF and Eulerian multiphase models in the documentation? You'll need R19 for this, but the sections on Multiphase will answer most of your questions re the boundary conditions.
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