We show by numerical simulations that the (\mathrm{CO}) distribution in the coma of Comet (\mathrm{P} /) Halley as measured by neutral gas mass spectrometer aboard Giotto spacecraft (P. Eberhardt et al., 1987, Astron. Astrophys. 187, 481-484) can be explained by an extended jet source originating from vent 1 in the rotational model of M. J. S. Belton et al. (1991, Icarus 93, 183-193). This is an alternative interpretation for the origin of the (\mathrm{CO}) distribution where Eberhardt et al. (1987) explained the observations in terms of a spherically symmetric extended source function. We still find nearly (\frac{1}{3}) of CO is due to CO sublimating directly at the nucleus, possibly from the vent itself. Approximately (50 %) of (\mathrm{CO}) that originates in the extended jet source may be formed via photolysis of (\mathrm{H}_{2} \mathrm{CO}) while the rest can be due to (\mathrm{CO}) trapped in grain mantels and other (\mathrm{C}=\mathrm{O})-bearing molecules. The overall production rates of CO in the two models differ by less than (29 %). The prediction of the jet source model compares satisfactorily with the distribution of CO observed in the coma by the IUE satellite but unfortunately does not allow one to discriminate between the two models. 1994 Academic Press, Inc.