Metal Ball Detection

I am a student from mechanical background in my final year of college with a little knowledge of sensors and circuits and need a few ideas to solve this problem.
There exists a brass tube something of this sort as shown in image in which oil would be immersed, with a metal ball inside and the tube would be capped at both ends. I need to understand which kind of sensor I can use at the both ends which would tell me when the ball touches the end cap when that tube filled with oil is kept in a perpendicular direction.

I'll assume you have a metal ball in an oil-filled capped tube, and by "perpendicular", you mean vertical.
If the "metal" ball is steel/iron, then you can use a hall-effect sensor, magnet and flux-guide. The magnetic flux density will increase when the ball is in line with the flux guide. You can arrange it so that the output is maximal when the ball is touching the end cap.

Okay so I did a little google search and I think this would work just fine for me. Thanks!

You're welcome.