This invention provides an optical disk effective in both precision and productivity, and to a process for the manufacture thereof. It is determined as to whether a varying width of a position voltage PV representing absolute positional information relative to a varying width of a pulse count number CP representing relative positional information is larger than an varying allowable range. The process can be carried out at relatively high liquid hourly space velocities and preferably at relatively low hydrogen to hydrocarbon ratios to produce a reformed product having relatively high liquid yield and hydrogen content.