A method for estimating influx volumes (qi) of fluids to a production flow (F) in a well (Wr) with two or more influx locations (3) along the well - arranging tracer sources (4) with unique tracer materials (4m) in fluid communication with two or more of said influx zones (3), - each said tracer material (4m) having a predefined short duration release dose (Vt4) to the fluids in the well, - allowing said tracer sources (4) to release said tracer material (4m) to said fluids at a given release instant (tR), - after said release instant (tR), consecutively collecting samples (c1, c2, c3,...) of said production flow (F) at the topside, - analysing said samples (c1, c2, c3,...) for identifying types of tracer material (4m) and concentration of said identified tracer materials (4c), - based on said concentrations (4c, 41c, 42c, 43c) and their sampling sequence and the well geometry, sequence of said separate influx zones, calculating said influx volumes (qi) from transient flow models - using the calculated influx volumes (qi) as parameters for controlling the production flow or for characterizing the reservoir.