To understand the meaning and differences between A,B & C operator.?

Question

I used to see in the job application website and noted that in the oil/gas industries, at most time they are looking for different level of production operators. It stated as A Operator, B operator or C operator. I don't know what exactly it means being an oil/gas production operator like me. I would be much appreciated if any one can detail out what it means?
Thanks.

Answer 1

I've worked in manufacturing (not oil/gas) for 13 years and never heard of A, B and C operator as a skill-level sort of description. The only reference that popped into mind was A shift, B shift, and C shift...meaning it isn't skill level but what hours of the day/days of the week you work.

If it is describing skill level, it must be specific to the company/industry.