Most/least profitable types of bulk transport payloads?

Can anyone tell me what are the most profitable and least profitable types of bulk payloads from a trucker / trucking company perspective? I'd like to know how much a trucker gets paid or a trucking company earns from hauling each ton/gallon/mile/etc for a customer. Thanks!

 

Thanks King Q. Can you tell me how much can be charged for hauling that stuff? I believe your currency is the Rand, is it charges by ton-mile, cpm, mile, per shipment? I'm just getting starting to learn more about the industry (in fact, I'll be getting a commercial driving license within the next year, probably, but only for private business, not for for-hire purposes).