An analysis of zero-first and first-first order reaction schemes has been carried out in a fluidised bed with a view to optimising the production of intermediate R for a given bubble diameter. For the zero-first order reaction sequence, the gas residence time at which the maximum concentration of R occurs is shown to be fixed and independent of bubble size in the bed. On the other hand, for a first-first order reaction scheme, an optimum gas residence time exists for the concentration maximum to occur at the bed exit. This interaction between bubble diameter, gas residence time and maximum concentration of intermediate is resolved by recourse to a three dimensional diagram which optimises the production of intermediate for any given value of bubble diameter or gas residence time. © 1981.