It is assu­med that medi­cal gui­de­lines spe­ci­fy the appro­pria­te amount of a divi­si­ble good which each indi­vi­du­al should recei­ve. Indi­vi­du­al requi­re­ments and pro­ba­bi­li­ties that the tre­at­ment is suc­cessful if an appro­pria­te amount is recei­ved dif­fer. The same appli­es to the suc­cess pro­ba­bi­li­ties if indi­vi­du­als are ina­de­qua­te­ly trea­ted. If sup­p­ly is insuf­fi­ci­ent to ser­ve all with appro­pria­te amounts an allo­ca­ti­on decis­i­on is neces­sa­ry. We defi­ne pro­ba­bi­li­stic allo­ca­ti­on rules that allo­ca­te chan­ces of suc­cessful tre­at­ment to all indi­vi­du­als. We ana­ly­se a spe­ci­fic ran­dom allo­ca­ti­on rule that assigns maxi­mal equal gains of chan­ces. We cha­rac­te­ri­ze the equal gain rule axiomatically.