There are only 2 types of commodity related businesses that are investment grade. One is companies that MOVE commodities. This includes pipelines and to a certain extent rails (altho they are technically industrials) like Enbridge, Kinder Morgan, CN, etc. The other is companies that are super diversified, either via vertical integration like Exxon, Suncor, Chevron, or via product type, like BHP.
Everything else is highly speculative. Some people may have a spot in their portfolio for that, but expect to lose your shirt once in a while when the bust cycle inevitably comes around.