An experiment conducted in 1975 tested the effects of two policy changes in five Oklahoma County Library System bookmobiles: (1) conversion to predominantly paperback collections; and (2) relaxation of overdue policies. There were two indicators of success: (1) the bookmobiles experienced a 26% increase in circulation during the year; and (2) the number of materials circulated and not returned proved cost-effective in terms of the value of paperback materials lost in circulation versus the predictable loss rate of hardbound materials. Data are summarized and policy implications discussed. (EMH)