Abstract This paper explores the expense preference behaviour in Colombian financial cooperatives. Our findings indicate that small cooperatives seem to use a production technology that is different from that of large ones, high-leverage cooperatives appear to use a technology that is different from that of low-leverage cooperatives, and managers of larger units exhibit separable-expense behaviour, while managers from lower-leverage units exhibit joint-expense preference behaviour. These results suggest that, in Colombia, a merger of small cooperatives into larger ones is a decision that should either not be promoted or carefully analyzed before being taken, in order to clearly detect all the possible benefits that might counterbalance managers' expense preference behaviour.