From Marketwatch:
We’re only a year and a half into the current period of low oil prices, but if you assume this will go on forever, you may be leaving quite a bit of money on the table.
One way to play a long-term recovery for oil, and that means having the guts to make what could easily be a five-year play, would be to start small and accumulate more if prices continue to decline. You might make a relatively conservative long-term bet by purchasing stocks of huge integrated oil companies that are still profitable, have plenty of cash and are sure to scoop up assets on the cheap before oil rebounds.