An oxygen sensor (1, 2, 3, 4, 5) configured for electrochemical determination of a concentration of dissolved oxygen in a liquid medium, said oxygen sensor (1, 2, 3, 4, 5) comprises: a working electrode configured to be in contact with said liquid medium; a reference electrode configured to be in contact with said liquid medium and having i) a surface area that is equal to or larger than a surface area of said working electrode, and ii) a surface made of Ag/AgCI, wherein said oxygen sensor (1, 2, 3, 4, 5) does not comprise any dedicated counter electrode; a retaining circuitry (10, 20, 30) configured to temporarily retain a floating voltage between said working electrode and said reference electrode; a measurement voltage circuitry (11, 21, 31) comprising a voltage source configured to apply a measurement voltage between said working electrode and said reference electrode during a first measurement period causing dissolved oxygen in said liquid medium to react by reduction at a surface of said working electrode to produce an evoked current into said working electrode; a floating voltage circuitry (12, 22, 32) configured to apply a voltage between said working electrode and said reference electrode equal to said temporarily retained floating voltage during a second measurement period immediately following and of an equal duration as said first measurement period to produce a current out from said working electrode; and a generating circuitry (13, 23, 33, 53) configured to generate a signal representative of said concentration of dissolved oxygen in said liquid medium based on a measured net charge to said working electrode equal to a sum of a charge transferred to said working electrode during at least a last part of said first measurement period and a charge transferred to said working electrode during at least a last part of said second measurement period. a working electrode configured to be in contact with said liquid medium; a reference electrode configured to be in contact with said liquid medium and having i) a surface area that is equal to or larger than a surface area of said working electrode, and ii) a surface made of Ag/AgCI, wherein said oxygen sensor (1, 2, 3, 4, 5) does not comprise any dedicated counter electrode; a retaining circuitry (10, 20, 30) configured to temporarily retain a floating voltage between said working electrode and said reference electrode; a measurement voltage circuitry (11, 21, 31) comprising a voltage source configured to apply a measurement voltage between said working electrode and said reference electrode during a first measurement period causing dissolved oxygen in said liquid medium to react by reduction at a surface of said working electrode to produce an evoked current into said working electrode; a floating voltage circuitry (12, 22, 32) configured to apply a voltage between said working electrode and said reference electrode equal to said temporarily retained floating voltage during a second measurement period immediately following and of an equal duration as said first measurement period to produce a current out from said working electrode; and a generating circuitry (13, 23, 33, 53) configured to generate a signal representative of said concentration of dissolved oxygen in said liquid medium based on a measured net charge to said working electrode equal to a sum of a charge transferred to said working electrode during at least a last part of said first measurement period and a charge transferred to said working electrode during at least a last part of said second measurement period.