In recent years aeronomic considerations of the value of the O+-O collision cross-section (QO+-O) in the ionospheric F-region have resulted in many values of a multiplicative adjustment factor (F) to the standard value of QO+-O which had been in use from the mid sixties to the late eighties. QO+-O and oxygen concentration ([O>) appear as a product in aeronomic calculations, so F can also be considered a multiplicative factor for the oxygen. [O> derived at EISCAT for data from 1984 to 1997 is compared to oxygen predicted by MSIS and values of F are calculated as a function of solar cycle and year. There is a solar cycle variation, with F varying from .65 at solar minimum to 1.18 at solar maximum. For solar fluxes between 100 and 160 solar flux units F at EISCAT is in good agreement with a value of F calculated for MSIS. No long term trend in the relationship between EISCAT [O> and MSIS [O> was found. ¿ 1998 American Geophysical Union