In this chart we can see the relationship between XOM and PBR. Take a look at the black line (the US dollar index) and the red line (XOM/PBR). We can see how the two lines have a close correlation. In my opinion, this relationship could be very useful to decide in which stock you should be invested. I think that (may be) the US dollar index can anticipate this relationship.
Time to sell PBR and buy XOM? May be. The next days I will be following this relationship.
In addition, a long term look at XOM. It is over an important tendency line, which was effective since 2002. Also, pay attention to the red line (9 EMA) and the yellow line (22 EMA), which give a buy signal in October 2009 and it is still valid (in the weekly chart).
Short term look: