BEIJING - Some supposedly edible cooking oil on store shelves in Beijing, Tianjin and Hebei province is being produced from so-called gutter oil and swill-cooked oil, Chinese media have reported.

Swill-cooked oil is waste animal oil and oil that has been used several times - usually by restaurants - for frying.

According to Beijing Times, some producers of the illegal cooking oil that is made from the gutter oil and swill-cooked oil are processing nearly 100 tons of their substandard and possibly dangerous oil each day. Their advanced refining equipment and production techniques make it difficult for buyers to tell which oil is produced properly and which is really processed garbage.