I was interested in knowing which companies do this, I know shell does, and also, duke energy.... What others?
You'll find that every major and minor oil company will trade the markets in varying degrees. Most of the majors will have a dedicated department who are just there to trade. Most of the minors will 'hedge' their requirements and take that as an opportunity to trade either by getting in early or waiting.
This is exactly right. I've worked for a boutique energy firm for 7 years now and every energy company we've come across trades. There are players out there that will buy an asset just to they can trade around it (e.g. utility, NYMEX book, etc.), and there will be highly aggressive firms that spec trade. In my experience it was surprising to see how much spec trading the integrated oil companies do on a daily basis.
look at the member list of OTC products on ICE and NYMEX clearport. many utility companies (Power/Gas) trade. check out ISO, ERCOT, oasis on google