  The NRO-OVRO CO imaging survey showed that molecular gas was more
concentrated to the central kiloparsec in barred spiral galaxies than in their
unbarred counterparts. The result provided not only evidence for bar-driven gas
transport but also estimates on the mean rate of gas transfer and lower limits
to the lifetime of bars. Other lines of evidence for the bar-driven transport
of ISM in spiral galaxies are summarized. They are complementary with each
other.
