Three pigeons were exposed to 1-hr and 4-hr sessions during which they earned food under a fixedratio 50 schedule of reinforcement while obtaining additional food according to either a variableinterval or a variable-time schedule. Postsession food was provided after the 1-hr sessions. The frequency of the variable-interval and variable-time food presentations was varied under the two session durations. The various combinations of within-session earned and unearned food, as well as the postsession food, defined conditions on the open-to-closed economy continuum. Key pecks tended to increase as the frequency of either variable-interval or variable-time food decreased. An economiccontinuum analysis based on an independence quotient as a measure of response-reinforcer independence is presented to account for the effects.