Following the tragic gas explosion in San Bruno, which has killed 4 people and devastated numerous homes, PG&E has been ordered to inspect their gas lines. The California Public Utilities Commission (CPUC) ordered PG&E to first inspect pipelines in highly populated areas. PG&E is to report its findings on or before October 12, 2010.
Anyone who smells gas in their area should call PG&E immediately to make a report; you should also call 911 so that the fire department can also be alerted.
You can find where gas lines are located, and whether there are any major gas lines near you by visiting the National Pipeline Mapping System at www.npms.phmsa.dot.gov (note: the website has been crashing regularly after the San Bruno incident).
There have been several gas explosions in the past involving PG&E. In 2005, a house in Los Altos exploded, with a man and his two children inside. Read more about that explosion here:https://www.sfgate.com/bayarea/article/Dad-trapped-2-children-injured-after-home-gas-2624121.php.