Selectivities to carbon monoxide higher than 90% for conversions of methane greater than 10% were obtained from the partial oxidation of methane on stoichiometric strontium hydroxyapatite (SrHAp1.67) at 873 K during 6 h on stream. However, the activities decreased gradually with increasing the time-on-stream to 78 h due to the transformation of the apatite to Sr-3(PO4)(2). With small quantities of tetrachloromethane (TCM) added to the feedstream, the high selectivity to CO was retained while the conversion suffered a marked decrease with increasing the times-on-stream. In the presence of TCM the catalytic solid consists of a complex mixture of hydroxyapatite, chlorapatite, phosphate and chloride, each of which contributes dissimilarly to the catalytic process.