Sec. 5. (a) As used in this chapter, "petroleum" means all hydrocarbons produced at a well in a liquid or gaseous state.
(b) As used in this chapter, "natural gas" means petroleum that maintains a gaseous state at atmospheric conditions.
(c) As used in this chapter, "oil" means petroleum that maintains a liquid state at atmospheric conditions.
(d) As used in this chapter, "barrel of oil" means forty-two (42) U.S. gallons of oil at sixty degrees Fahrenheit (60° F).