A method for tracing a tracer compound in a fluid system, said tracer compound comprising two or more polyether alcohol compounds, a first part of said fluid system comprising an upstream part of a fluid conduit, a second part of said fluid system comprising a downstream part of said fluid conduit, said fluid conduit being in a petroleum production well, - providing the two or more truly monodisperse polyether alcohol compounds, - each of said two or more truly monodisperse polyether alcohol compounds comprising more than three monomer groups, and each of said two or more truly monodisperse polyether alcohol compounds having one or more functional groups - preparing said two or more truly monodisperse polyether alcohol compounds for being released to said first part of said fluid system upon a predetermined change in said fluid system's conditions, by adding one or more functional groups to said truly monodisperse polyether alcohol compounds, wherein said functional groups are increasing the hydrophilicity of said truly monodisperse polyether alcohol compounds, or wherein said functional groups are increasing the lipophilicity of said truly monodisperse polyether alcohol compounds, thus preparing said two or more of said truly monodisperse polyether alcohol compounds for being released to said first part of said fluid system upon a predetermined change in said fluid systems conditions - arranging said one or more functional groups for releasing said truly monodisperse polyether alcohol compound to the first part of the fluid system - placing said two or more truly monodisperse polyether alcohol tracer compounds in contact with said first part of said fluid system, - taking a sample from said second part of said fluid system, - analysing said sample using an apparatus for determining the presence or not of said two or more of said truly monodisperse polyether alcohol compounds in said fluid sample. - providing the two or more truly monodisperse polyether alcohol compounds, - each of said two or more truly monodisperse polyether alcohol compounds comprising more than three monomer groups, and each of said two or more truly monodisperse polyether alcohol compounds having one or more functional groups - preparing said two or more truly monodisperse polyether alcohol compounds for being released to said first part of said fluid system upon a predetermined change in said fluid system's conditions, by adding one or more functional groups to said truly monodisperse polyether alcohol compounds, wherein said functional groups are increasing the hydrophilicity of said truly monodisperse polyether alcohol compounds, or wherein said functional groups are increasing the lipophilicity of said truly monodisperse polyether alcohol compounds, thus preparing said two or more of said truly monodisperse polyether alcohol compounds for being released to said first part of said fluid system upon a predetermined change in said fluid systems conditions - arranging said one or more functional groups for releasing said truly monodisperse polyether alcohol compound to the first part of the fluid system - placing said two or more truly monodisperse polyether alcohol tracer compounds in contact with said first part of said fluid system, - taking a sample from said second part of said fluid system, - analysing said sample using an apparatus for determining the presence or not of said two or more of said truly monodisperse polyether alcohol compounds in said fluid sample. <EOS>