If integrateds and oil-and-gas operations are put together in one category, it would make up the largest group in the Low P/E Bin. The mock fund that approximates an index fund, the Statistical Low P/E Fund, has about 33% of its assets in the Energy sector.
Both the integrated oils and oil-and-gas operations are a naive quant's dream. Of the eighteen companies in both industries that are in the Low P/E Bin, all but two of them have double-digit continuing-operations EPS growth. With the exception of Petrobras, Repsol and Baytex, that growth rate spans ten years. For those whose return rate on common equity is meaningful, these companies have a minimum of 15%...and 20+% isn't uncommon.
The Low P/E Bin contains so many of them because of the burst crude bubble, and because natural gas is going nowhere. Buying into the oils is largely a recovery play, but there are some oil bulls who count on inflation to get crude back up. There hasn't been much so far, but recent money supply growth indicates that there will be down the road.
More exotically, there is a group of oil bulls who adhere to "Peak Oil" theory. In essence, that theory predicts that the world is slowly running out of oil over and above what new supplies can replace. Consequently, world production of oil is forecasted to drop in the teeth of rising world demand as growth comes back. These two forces will push oil prices way above present levels.
Peak Oil theory is controversial, as it resembles similar end-of-oil predictions made all through the twentieth century. Tying it to doomsday scenarios is even more controversial, as natural gas can be substituted for oil in many energy applications; coal will do for some. The U.S. has been called the "Saudi Arabia of Coal," and natural gas is plentiful from North American sources.
In my opinion, what'll primarily get oil back on the bull track is inflation. A return of some world growth will amplify it, but future inflation seems a surer call at this point.