A process comprising: a) introducing into a reaction zone; i) ethylene, ii) a catalyst system comprising (a) a chromium component comprising an N 2 -phosphinyl amidine chromium compound complex, an N 2 -phosphinyl formamidine chromium compound complex, an N 2 -phosphinyl guanidine chromium compound complex, or any combination thereof, and (b) an aluminoxane, iii) the organic reaction medium, and iv) optionally hydrogen; and b) forming an ethylene oligomer product in the reaction zone; wherein: the reaction zone contains a C 3+ olefin and optionally an organic reaction medium wherein the reaction zone is substantially devoid of ethylene, and wherein over a reaction zone period of time the reaction zone has a C 3+ olefin:ethylene weight ratio that decreases from a value of at least 0.5:1 to a value less than 0.2:1, and wherein the C 3+ olefin in the reaction zone and the C 3+ olefin of the C 3+ olefin:ethylene weight ratio is not an ethylene oligomer formed in-situ within the reaction zone; or the ethylene, the catalyst system, and the organic reaction medium, and optionally hydrogen, are introduced into the reaction zone and contacted in the reaction zone, and for a C 3+ olefin/ethylene feed period of time a C 3+ olefin is introduced into the reaction zone, wherein over a reaction zone period of time the reaction zone has a C 3+ olefin:ethylene weight ratio that decreases from a value of at least 0.5:1 to a value less than 0.2:1, and wherein the C 3+ olefin in the reaction zone and the C 3+ olefin of the C 3+ olefin:ethylene weight ratio is not an ethylene oligomer formed in-situ within the reaction zone. a) introducing into a reaction zone; i) ethylene, ii) a catalyst system comprising (a) a chromium component comprising an N 2 -phosphinyl amidine chromium compound complex, an N 2 -phosphinyl formamidine chromium compound complex, an N 2 -phosphinyl guanidine chromium compound complex, or any combination thereof, and (b) an aluminoxane, iii) the organic reaction medium, and iv) optionally hydrogen; and i) ethylene, ii) a catalyst system comprising (a) a chromium component comprising an N 2 -phosphinyl amidine chromium compound complex, an N 2 -phosphinyl formamidine chromium compound complex, an N 2 -phosphinyl guanidine chromium compound complex, or any combination thereof, and (b) an aluminoxane, (a) a chromium component comprising an N 2 -phosphinyl amidine chromium compound complex, an N 2 -phosphinyl formamidine chromium compound complex, an N 2 -phosphinyl guanidine chromium compound complex, or any combination thereof, and (b) an aluminoxane, iii) the organic reaction medium, and iv) optionally hydrogen; and b) forming an ethylene oligomer product in the reaction zone; the reaction zone contains a C 3+ olefin and optionally an organic reaction medium wherein the reaction zone is substantially devoid of ethylene, and wherein over a reaction zone period of time the reaction zone has a C 3+ olefin:ethylene weight ratio that decreases from a value of at least 0.5:1 to a value less than 0.2:1, and wherein the C 3+ olefin in the reaction zone and the C 3+ olefin of the C 3+ olefin:ethylene weight ratio is not an ethylene oligomer formed in-situ within the reaction zone; or the ethylene, the catalyst system, and the organic reaction medium, and optionally hydrogen, are introduced into the reaction zone and contacted in the reaction zone, and for a C 3+ olefin/ethylene feed period of time a C 3+ olefin is introduced into the reaction zone, wherein over a reaction zone period of time the reaction zone has a C 3+ olefin:ethylene weight ratio that decreases from a value of at least 0.5:1 to a value less than 0.2:1, and wherein the C 3+ olefin in the reaction zone and the C 3+ olefin of the C 3+ olefin:ethylene weight ratio is not an ethylene oligomer formed in-situ within the reaction zone.