Abstract: In this paper, electrospray ionization mass spectrometry has been used for the rapid analysis of petroleum sulfonates for enhanced oil recovery (EOR). The molecular weight distribution range, average molecular weight and main structure types of petroleum sulfonates can be confirmed. Through examining the ionization efficiency of eight commonly used solvents on petroleum sulfonates, it shows that 50% methanol-water solution has the maximum sensitivity for the ionization of petroleum sulfonates. The results showed that the molecular weight distribution range of the petroleum sulfonates from Shengli Oilfield is from 200 to 600, the number-average molecular weight is 488 and the weight-average molecular weight is 534. The main components of Shengli petroleum sulfonates are alkylbenzene sulfonate, alkylnaphthalene sulfonate and alkylindane sulfonate. A distinguishing analysis for petroleum sulfonates from Shengli, Daqing, Karamay and Yumen oil fields has also been carried out.