Abstract: A multifilament sheet, tow or web of acrylonitrile precursor fibres are passed through a pre-heat zone at a temperature at least 100.degree. C below the critical temperature. The material is then passed through a two-stage oxygenation zone comprising a first stage at 220.degree. to 250.degree. C and a second stage at 260.degree. to 300.degree. C. The material passes straight through the oxygenation zone and is held in sufficient uniform tension to stretch the fibres during heating and oxygenation. The oxygenated material is then passed through a carbonizing zone comprising at least one stage at 1050.degree. to 1600.degree. C under non-oxidizing conditions. The resulting carbon fibre has a mean Young's modulus of at least 25 .times. 10.sup.6 p.s.i. and a mean tensile strength of at least 250,000 p.s.i.