The paper describes an extensive program to define the effects of operating and maintenance practices on the transfer efficiency of spray painting. Three spray painting systems were used: air-atomized conventional, air-atomized electrostatic, and airless conventional. More than 30 operating variables were initially identified and evaluated. Eight were found to be most important and received intensive testing: restricted air lines, booth air rate, gun cleanliness, restricted paint lines, fan or shaping air, gun tip erosion, electrode position, and tip voltage.