Petroleum's Replacement to Be as Expensive as Petroleum

That's about it. The price of corn is increasing because of its use in the creation of ethanol (among other factors). It will probably be easy for Big Oil to become Big Corn or Big Water or Big Sun, depending on the successor to petroleum (and petroleum-related accessories) to fuel or mechanical engines.

The scariest would have to be a water cartel, as an industry to profit directly from the sun seems ridiculous (unless you are Montgomery Burns).