Bhai jaan solution se pehlay yeh to poch lo keh kitna kam ho raha hai oil.
Regarding 2 number oil, Its not only zic, its shell, caltex, total every such name which is popular.
So, whichever oil u buy, try to purchase from very reputed dealer.
Oil kam kitna ho raha hai? Aur kitnay KM baad? Gaari ki total mileage kia hai? Gaari ziada long route per chalti hai ya shehar main? Without knowing all these things no one can suggest suitable solution.