We explore the sensitivity of terrestrial CO2 flux estimates from a specific inversion methodology, based on the configuration of Fan et al. [1998] , to different configurations of the global observation network. Using diagnostics derived from the inversion equations, we focus on quantifying the relative influence of individual stations on the flux estimates. We also examine the impact of different assumptions for the data uncertainty values by contrasting weighted and unweighted inversions and presenting related sensitivity analyses. For this particular methodology, unweighted estimates of continental scale fluxes prove very sensitive to network configuration. The inclusion or omission of a few important stations in and around the northern continents can result in shifts in continental-scale flux estimates of up to 1.5 Gt C/year. The weighted estimates are less sensitive to network configuration. Diagnostics of relative station influence indicate that this results from the reduced roles of previously influential continental sites; i.e., those stations characterized by high levels of data uncertainty. In the weighted approach, stations on continental peripheries associated with lower levels of data uncertainty are the most important in determining terrestrial fluxes. Finally, using the diagnostics of relative station influence, we discuss potential sampling strategies for the determination of regional fluxes from surface measurements.