US oil fell 3.1% to $39.62 today, but has mostly hung near $40 for the last month. So why did energy stocks suffer another severe meltdown? Thurs:  Phillips $PSX -7.8% Marathon $MRO -7.1 Conoco $COP -6.6 $EOG -6.5 Occidental $OXY -5.8 Chevron $CVX -4.2 Exxon $XOM-4.1  SandP500 -0.6