I-petroleum gas ehlanganisiwe (i-APG), noma igesi ehambisanayo, uhlobo oluthile lwegesi yemvelo etholakala ngokufakwa kwephethiloli, okungenzeka kuncibilike emafutheni noma "njengekepisi yegesi" yamahhala ngaphezu kwamafutha echibini. Igesi ingasetshenziswa ngezindlela eziningi ngemuva kokucutshungulwa: ithengiswe futhi yafakwa kumanethiwekhi okusabalalisa igesi yemvelo, asetshenziselwa ukukhiqizwa kukagesi esizeni ngezinjini noma ophephela, abuyiselwe ukubuyiselwa kwesibili futhi asetshenziswe ekuvuseleleni uwoyela okwenziwe ngcono, aguqulwa esuka kugesi oketshezini okhiqiza okokubasa okwenziwe, noma okusetshenziswa njenge-feedstock yomkhakha we-petrochemical.