Do you put a comma before the word 'and' in a list of three things?
In my formal English grammar lessons, (I'm English) I was taught never to put a comma before the word 'and'. However, it is commonly used and you can find it in lots of newspaper articles etc.
But for lists of objects:
'He bought some apples, pears, bananas and satsumas.' I would say that you definitely should not use a comma here.
The comma before "and" or "or" is called the "Oxford comma". Some publications insist on it.
If your editor/teacher/professor/whatever does not give you any rules regarding the use of the Oxford comma, then my personal preference would be to use it when it avoids ambiguity:
"The two companies in question are Grabbit and Dodgem and Runne."
Hmm. What are the names of the companies? Do you mean:
"Grabbit, and Dodgem and Runne"
"Grabbit and Dodgem, and Runne"?