The present invention relates to a a continuous process for producing carbon fibrils by decomposing a source of carbon at elevated temperatures in contact with a multivalent metal and recovering the fibrils formed thereby comprising the steps of introducing catalyst particles having a size of up to 400 µm (microns) and comprising at least one multivalent transition metal on a particulate substrate into a reactor heated to a temperature of 500°C to 1500°C, and recovering the fibrils formed thereby wherein said metal is present on said substrate as a multiplicity of discontinuous catalytic sites which, at least during fibril formation, have a size of 3,5 to 70 nm (35 to 700 Å) which size is measured by measuring the size of the transition metal particles recovered along with produced fibrils. This invention also relates to a reaction apparatus to be used for carrying out said process.