Well I will put it this way, they only make one grade of Pennzoil. We will take 5W30 for an example. When they blend a batch so much is dedicated for quart bottles, gallon jugs, 5- gallon pails, 55-gallon drums, and bulk delivery. When bulk oil is being shipped out to a company branch or a distributor it is either shipped by tanker truck or by rail. Before those tankers and rail cars are filled, they have to meet a clean standard which is very very strict. You can be sure the oil shipped is the exact same quality as the packaged product. Now saying all that, it is up to the local branch or distributor to keep their bulk tanks under the same standards. I know that Shell pulls samples from each of it's branch locations and distributors every quarter to test the quality of the oil. I have seen distributors cancelled for not maintaining quality standards. Then to carry it further, the branch or distributor delivers bulk product to car dealers, lube centers, repair shops, etc. I can't say what they do now, but I use to go to all of the customers in my area and pull samples at least twice a year to send samples in for testing.
MGregoir is correct about the Mobil products. Drive Clean is what Mobil sells to car dealers and lube centers in bulk and it is a totally different product than the Mobil Clean 5000.