A fugitive gas capture system includes a variable volume gas storage assembly (e.g., a bag) that captures gas from headspace of a production tank. The variable volume storage assembly has a first state and a second state corresponding to first position and a second position, respectively, where the first state represents a greater volume of captured gas being stored than a volume of captured gas stored in the second state. A back pressure regulator is included between the variable volume storage assembly and the production tank to backflows gas from the variable volume storage assembly back into the headspace of the production tank.