Abstract: The efficiency and accuracy of a peristaltic pump is increased simply and inexpensively by controlling the cross sectional configuration of the section of flexible tubing which is operated upon the pump thrust members during a pumping operation. Specifically, the section of tubing, which is normally generally cylindrical in configuration, is held partially constricted or compressed upon being mounted in the pump, so that it becomes generally oval in cross sectional configuration. The thrust members of the pump, when the latter is operating, thus repeatedly compress a section of tubing which is already partially compressed, and which never is allowed to expand fully back to its cylindrical configuration. This substantially reduces the drop in feed rate heretofore experienced by similar pumps because of tubing fatigue and augument.