We studied competitive adsorption of ethyl xanthate (C2X) and amyl xanthate (C5X) on an aqueous suspension of chalcopyrite particles. We first investigated their chemi- and physisorption separately and then explored whether there was any difference in the bonding strengths of the chemisorbed cuprous xanthate complexes with C2X and C5X. Further, we monitored the competition between C2X and C5X in chemi- and physisorption on the chalcopyrite surface using different C2X and C5X binary solutions. It was found that prechemisorbed C2X can be desorbed and replaced by postadded CSX but that prechemisorbed C5X cannot be replaced by postadded C2X. This clearly indicates that the bonding strength of the cuprous xanthate complex is much higher for C5X than for C2X. When C2X and C5X are simultaneously added to the chalcopyrite suspension, CSX is chemisorbed first, and only when C5X cannot cover the full surface is C2X chemisorbed. An adsorption phase diagram is defined that describes how the chemi- and physisorption occur in the C2X + C5X binary solutions.