When PSX was spun off from COP, the pps of PSX skyrocketed, doubled, in a short period of time. And during that time, the pps of COP was stagnant. However, during the last 12 months, both PSX and COP have each gained about 20%, in terms of their respective pps.
But, what is really telling is the results of the last six months. During that time, PSX's pps has lost about 14% of it's value, while COP's pps has gained about 18%. Moving ahead, it's becoming clear that COP offers a much greater chance for shareholder value than does PSX.
Both are very well managed companies and I own both. I do believe COP will outperform PSX in the long run. My investment ratio between the two is about 6 shares of COP for every 1 share of PSX. I sleep very well at night owning both.