  Galaxy-galaxy interactions and large scale galaxy bars are usually considered
as the two main mechanisms for driving gas to the centres of galaxies. By using
large samples of galaxy pairs and visually classified bars from the Sloan
Digital Sky Survey (SDSS), we compare the relative efficiency of gas inflows
from these two processes. We use two indicators of gas inflow: star formation
rate (SFR) and gas phase metallicity, which are both measured relative to
control samples. Whereas the metallicity of galaxy pairs is suppressed relative
to its control sample of isolated galaxies, galaxies with bars are metal-rich
for their stellar mass by 0.06 dex over all stellar masses. The SFRs of both
the close galaxy pairs and the barred galaxies are enhanced by ~60%, but in the
bars the enhancement is only seen at stellar masses M* >10^10 M_solar. Taking
into account the relative frequency of bars and pairs, we estimate that at
least three times more central star formation is triggered by bars than by
interactions.
