An ozone delivery system for delivering and manufacturing a measured amount of an ozone/oxygen admixture, which is able to measure, control, report and differentiate between delivered-ozone and absorbed-dose of ozone. Improved gas-fluid contacting devices that maximize gas-fluid mass transfer may be included. All gas contacting surfaces of the system, including one or more gas-fluid contacting devices are made from ozone-inert construction materials that generally do not absorb ozone or introduce amounts of contaminants or deleterious byproducts of oxidation into a fluid or non-fluid target from ozone oxidation.