How do easements work with gas lines on new construction?
Below is some info from a typical natural gas utility. From reviewing this, I gather (at least with this utility) that they are very familiar with the complications related to this type of arrangement and have implemented specific safeguards to protect them from any liability stemming from disputes.

Is it typical for your property to have a gas-main, and have no easements?

YES, for normal &quot;single-lateral&quot; residential service arrangements; however, they have a defacto easement in that you agree to always allow access to their equipment which includes everything from the street main up to and including the meter.

Defacto easement: When I had the utility company extend the line to the house, do they have an easement automatically right up to the house? Maybe I didn't read the small print...

YES, they have a &quot;defacto easement&quot; up to and including the meter.
NOTE- for your situation (Cross Lot Branch Service) it is likely that there is an actual easement that was obtained from you and/or your neighbor (or previous owners) to allow the shared line to cross both properties.