High ambient interstellar pressure is suggested as a possible factor to explain the ubiquitous observed growth-rate discrepancy for supernova-driven superbubbles and stellar wind bubbles .
Pressures of P / k \sim 10 ^ { 5 } { cm ^ { -3 } K } are plausible for regions with high star formation rates , and these values are intermediate between the estimated Galactic mid-plane pressure and those observed in starburst galaxies .
High-pressure components also are commonly seen in Galactic ISM localizations .
We demonstrate the sensitivity of shell growth to the ambient pressure , and suggest that superbubbles ultimately might serve as ISM barometers .