1993 Blazer K1500 running rich

My Blazer, 4WD 180K miles, is running rich judging by heavy soot on the tailpipes and MPG of 10-11. Could it be a bad O2 sensor? It has throttle body injection, catalyst status unknown(it has one still)

Any ideas?[img:6f1b359d88]http://www.2carpros.com/forum/automotive_pictures/73637_DSCF0017_1.jpg[/img:6f1b359d88]