CNG oils are recomended to be changed at 3000 kms, which i tend to use abt 5000kms,
while normal petrol engines oils can be used for 5-7k miles,
while synthetic oil (orignal) dunt bother u atleast for 10k Kms, sum people say 15,000 but 9k is safe. as by then the car completes 5 to 7 months.