In this paper, undoped and LaOCl-doped SnO2 nanofibers were prepared by a simple one-step electrospinning technique and their responses upon exposure to CO2 gas in different oxygen containing backgrounds were systematically investigated. It was observed that the obtained nanofibers were hollow porous structures that gave rise to excellent performance. The sensor based on 8 at.% LaOl-SnO2 nanofibers exhibited optimal response (R-gas/R-air =3.7) toward 1000 ppm CO2 at 300 degrees C with response/recovery times of 24 s/92 s, and didn't show any saturation over a wide range of CO2 concentrations (100-20000 ppm). In terms of the sensing behavior of these sensors, their sensing mechanisms are proposed as follows: (1) In low oxygen concentration background, CO2 primarily reacts with V-O(center dot center dot), which needs high activation energy to occur, so only a slight number of CO2 can take part in the reaction. (2) In high oxygen concentration background, CO2 mainly reacts withO(O)(X). Since this reaction conducts easily, CO2 can react with O-O(X) sufficiently. The proposed sensing mechanisms can help readers better understand the role oxygen plays in CO2 gas sensing process. (C) 2016 Elsevier B.V. All rights reserved.