FTIR spectra of inclusions sampled from fault-zone reservoirs of the northwestern Junggar Basin show that water, with different abundances, does exist in petroleum inclusions. It is thus implied that petroleum inclusions can seldom form without water. Different inclusions hosted in one single grain, and formed in one oil charging phase, have a largely varied ratio of water to oil and slightly changed CH3/CH2 ratio. This likely provides evidence for fault-related episodic migration and accumulation of hydrocarbons. FTIR spectra of inclusions sampled from fault-zone reservoirs of the northwestern Junggar Basin show that water, with different abundances, does exist in petroleum inclusions. It is thus implied that petroleum inclusions can seldom form without water. Different inclusions hosted in one single grain, and formed in one oil charging phase, have a largely varied ratio of water to oil and slightly changed CH3 / CH2 ratio.