The paper is aimed at studying the influencing factors of producing ultra-low interfacial tension (IFT) under alkali-free systems, including molecular structures as well as concentrations of double long-chain 1,3,5-triazine surfactants (A-DCTn-8, n = 8, 10, 12, 14), temperature, electrolyte, the property of oil phase, and mass ratios of surfactant homologues mixtures. It was found that only A-DCT10-8 and A-DCT12-8 could reduce IFTs to ultra-low value (<10 (2) mN m (1)) at wide surfactant concentration range against different oil phases. In addition, the dynamic interfacial tensions (DIFTs) of A-DCT10-8 and A-DCT12-8 could maintain ultra-low value under the conditions of higher temperature. The results might be of theoretic and realistic significance in the enhanced oil recovery. The DIFTs of A-DCT10-8 in increased with higher salinity. The effects of sodium chloride on DIFTs of A-DCT12-8 were not obvious, whereas the adding of a small quantity of sodium carbonate could lower its DIFTs up to 1-2 orders of magnitude. After investigating the DIFTs of A-DCT12-8/A-DCT8-8 mixtures with different mass ratios, we found that this kind of mixtures exhibited good synergism. This synergism reduced their DIFTs to ultra-low value and changed the time to reach minimum DIFT value. The minimum alkane carbon number (n(min)) of this kind of surfactants were also investigated, and it was found that the nmin of them were associated with their structures. (C) 2012 Elsevier Ltd. All rights reserved.