the refiners are usually very volatile and have been great trading vehicles for me. Part of the reason, I think, is that everyone is dumping the energy etf's, so the refiners get sold along with the others.
on the other hand, mpc fell more than many producers Friday. One reason could be that people think crude prices are near a bottom so the crack spread is likely to narrow going forward.
I bot some mpc at 51.12 on Friday and will add more if it drops to the mid 40's. also own psx and vlo