"General considerations relating to the use of analyses for determining depth-volatile relations in coalfields are discussed. New evidence from New Zealand is presented and British evidence reviewed. A maximum rate of downward decrease of volatiles is inferred at 23 per cent volatiles, and a depth-volatile band from 42 to 5 per cent volatiles is presented. British coal field sequences fit the band, rendering unnecessary the complex geological explanations for differing rates of downward decrease of volatiles given by previous authors. Tectonic pressure is rejected in favour of depth of burial as a cause of rank differences."