While referring to the cost of operations of a business, which is the right term to use?

a. operation cost

b. operating cost

c. operational cost

b seems to be most popular, while c appears to be grammatically correct. What do you think?
b. indeed.
Yes you're correct - operating costs - that's the term used in business English
Students: Are you brave enough to let our tutors analyse your pronunciation?
 Marius Hancu's reply was promoted to an answer.
Thanks for your inputs.

I searched for "operating" and "operational" on Google and found both being used. I am still not sure if there is some logic behind using one or the other in some specific places.