If they don't continue to invest in further exploration, they won't have anything to pump out of the ground 20 years from now. That would negatively affect their net present value right now, thus negatively impacting their stock price.
My point was that vilifying the oil companies is the easy out. The oil companies make less money per gallon of gas than the state and federal gov't tax. If we're unhappy with the price of gasoline (which is what we're really upset about, after all who cares how much money Exxon is making if gas is only $1 per gallon), then we should ask what is making gas expensive. I would suggest that the present cost reflects a variety of factors: increased demand as the world economy exits recession, reduced stability in the middle east, U.S. policy that is shutting down drilling in the gulf, denying permits in artic waters, and delaying/nixing U.S. canadian pipeline into the U.S. While we may be able to have some affect on middle east stability, the primary lever we can pull is domestic energy policy.
However, Obama himself stated in his campaign that gas prices need to rise, so why is he now attempting to vilify the capitalists? Doesn't the oil industry create high paying union jobs? I understand that oil is a fungible commodity, but cranking up our domestic production when oil is at $113/barrel would allow a lot of domestic operations with domestic workers to make a truck load of money, which positively affects the domestic economy and improves the employment picture. But the Obama adminisstration is doing the exact opposite. That guy may be a nice guy, but he's got a problem with capitalism. Problem is, without capitalists making a truckload of money, the unemployment rate won't go down. He's kinda in a catch-22. He wants the economy to grow, but he can't stand the possibility that those responsible for taking the risk to make the economy grow might get wealthy in the process.