Studies　on　radiosensitization　of　biological　damage　by　O2　began　about　a　century　ago　and　it　remains　one　of　the　most　significant　subjects　in　radiobiology.　It　has　been　related　to　increased　production　of　oxygen　radicals　and　other　reactive　metabolites,　but　only　recently　to　the　action　of　the　numerous　low-energy　electrons　(LEEs:　0-30　eV)　produced　by　ionizing　radiation.　We　provide　the　first　complete　set　of　G-values　(yields　of　specific　products　per　energy　deposited)　for　all　conformational　damages　induced　to　plasmid　DNA　by　LEEs　(GLEE　(O2))　and　1.5　keV　X-rays　(GX(O2))　under　oxygen　at　atmospheric　pressure.　The　experiments　are　performed　in　a　chamber,　under　humidity　levels　ranging　from　2.5　to　33　water　molecules/base.　Photoelectrons　from　0　to　30　eV　are　produced　by　X-rays　incident　on　a　tantalum　substrate　covered　with　DNA.　Damage　yields　are　measured　by　electrophoresis　as　a　function　of　X-ray　fluence.　The　oxygen　enhancement　ratio　GLEE(O2)/GLEE(N2),　which　lies　around　2　for　potentially　lethal　cluster　lesions,　is　similar　to　that　found　with　cells.　The　average　ratio,　GLEE(O2)/GX(O2),　of　12　for　cluster　lesions　and　crosslinks　strongly　suggest　that　DNA　damages　that　harm　cells　are　much　more　likely　to　be　created　by　LEEs　than　any　other　initial　species　generated　by　X-rays　in　the　presence　of　O2.