Absolute and differential chemical abundances are presented for the largest group of massive stars in M31 studied to date .
These results were derived from intermediate resolution spectra of seven B-type supergiants , lying within four OB associations covering a galactocentric distance of 5 - 12 kpc .
The results are mainly based on an LTE analysis , and we additionally present a full non-LTE , unified model atmosphere analysis of one star ( OB78-277 ) to demonstrate the reliability of the differential LTE technique .
A comparison of the stellar oxygen abundance with that of previous nebular results shows that there is an offset of between \sim 0.15 - 0.4 dex between the two methods which is critically dependent on the empirical calibration adopted for the R _ { 23 } parameter with [ O/H ] .
However within the typical errors of the stellar and nebular analyses ( and given the strength of dependence of the nebular results on the calibration used ) the oxygen abundances determined in each method are fairly consistent .
We determine the radial oxygen abundance gradient from these stars , and do not detect any systematic gradient across this galactocentric range .
We find that the inner regions of M31 are not , as previously thought , very ’ metal rich ’ .
Our abundances of C , N , O , Mg , Si , Al , S and Fe in the M31 supergiants are very similar to those of massive stars in the solar neighbourhood .