This paper explores the issue of expense preference behaviour in Colombian cooperatives. Cost data were analysed and statistical tests conducted to explore whether large cooperatives, when compared to small ones, and low leverage, when compared to high leverage, exhibit expense preference behaviour in the input labour. To carry out these tests the method described in Mester (1989) was employed. Our findings indicate that small cooperatives seem to use different production technology than large ones. Likewise, high leverage appears to use different technology than low leverage cooperatives. Managers of larger units exhibited separable expense behaviour: Larger in this case was not equivalent to better. With respect to the effect of financial leverage, lower leverage units exhibited joint expense preference behaviour. Although there are not studies in Colombia on the expense preference behaviour in cooperatives, this study come to terms with other studies on the efficiency of the Colombian financial system where evidence was found of the importance of the so called X Inefficiency. Leaving aside considerations of quality of services and focusing on costs, our findings indicate that, merger of small cooperatives into larger ones is a decision that either should not be promoted or must be carefully analysed before taken it to clearly detect all the possible benefits that might counterbalance to the expense preference behaviour exhibited by managers.