well that gauge doesn't tel you how much oil you have it tells you the pressure in the system. I would keep an eagles eye on that gauge and if it does drop to 0 STOP DRIVING IMMEDIATLY...
Change the oil pressure sending unit. It's right above the oil filter. I recently had the same experience with my car. Oil pressure gauge was starting to read low, and additionally, it was starting to a lot of oil leaking right around there. My problem was that oil pressure switch was no longer sealing, which is why it was leaking, and showing me incorrect oil pressure.