Osoro wuxuu wakiil ka ahaa Kenya laba jeer marxaladda adduunka ee 1991, isagoo ku tartamaya 1991 IAAF World Cross Country Championships (halkaas oo uu kaalinta shanaad ka galay tartankii dheeraa) ka dibna wuxuu ku tartamayaa 1991 World Championships in Athletics (oo laga saaray heerarka 5000 mitir oo leh farqi yar oo ka dhan ah Dionísio Castro). Si kastaba ha noqotee, wuxuu ku guuleystey billad 5000 m ah ciyaarihii All-Africa ee sannadkaas 1991. Wuxuu ka soo muuqday kooxda Kenyan World Cross Country markii labaad 1992 IAAF World Cross Country Championships
, in kasta oo uu ku guulaystay isku daygiisa, maadaama uu ku dhammeeyay kaalinta 23-aad. Waxyaabaha uu ku guuleystay waxaa ka mid ahaa tartanka caalamiga ah ee Belfast.