Clethodim is a non-residual, foliar-applied herbicide that controls grass weeds in many major and minor crops in the United States. Grass control was evaluated in field trials conducted in 2003 and 2004 using commercial clethodim formulations of Select (240 g/L), Arrow (240 g/L), and Prism (113 g/L), and experimental clethodim formulations of V-10117 (226 g/L), V-10139 (192 g/L), and V10137 (113 g/L). Petroleum oil (PO) adjuvant was added to all clethodim treatments except V-10137. The V-10137 formulation of clethodim without petroleum oil (PO) adjuvant gave greater and faster grass control than other formulations of clethodim with PO. Adding PO adjuvant to V-10137 reduced activity except at reduced rates when additional PO or nonionic surfactant increased grass control. All clethodim formulations except Prism and V-10137 caused significant canola injury when applied at post-bolting. V-10137, without additional adjuvants, with less active ingredient concentration, and likely a higher adjuvant load has more grass activity at equivalent rates than other clethodim formulations with PO. Tribenuron applied with clethodim antagonized grass control from Select, Arrow, V-10117, and V-10139, but not V-10137. Grass control was reduced from 99 % when clethodim formulations (except V-10137) were applied alone, to 50 %–80 % when applied with tribenuron. Grass control from V-10137 applied alone or with tribenuron, with or without PO, was greater than 96 %. The K salt of glyphosate was antagonistic to Select and V-10137, but V-10137 overcame most of the antagonism. These results suggest V-10137 activity is greater than commercial clethodim formulations of Select or Arrow, may not require additional oil adjuvant for grass control, is effective with glyphosate, and can overcome tribenuron antagonism. Including an oil adjuvant with V-10137 may not increase grass control in some uses.