The invention is a tracer method for online monitoring of downhole zonal contributions of oil, condensate, gas, or water mass flux (Foz, Fez, Fwz, Fgz) of a production flow (2) in a petroleum production well (1), comprising arranging distinct tracer carrier systems (Trsl, Trs2,..), each in different production zones (Zl, Z2,...) in said well, said distinct tracer carrier systems arranged for releasing unique tracers (Trl, Tr2,..) to a fluid of said production zones, said tracers having affinity after downhole release to separate phases of oil, condensate, gas, or water, using an online tracer monitor (5), conducting sampling of tracer concentrations (cl, c2,...) for at least one of the tracers in said zonal mass fluxes at a high sampling rate, based on said concentration values, estimating the corresponding zonal tracer fluxes for each delivery data point and using said one or more estimated zonal mass fluxes to control one or more Petro Technical processes.