Enhanced oil recovery by chemical flooding has been a main measure for postponing the overall decline of crude oil output in China, and surfactant polymer (SP) flooding may replace alkali surfactant polymer flooding in the future for avoiding the undesired effects of using caustic alkali. In this paper, a series of double alkyl non-ionic surfactants, 1,3-dioctyl glyceryl ether ethoxylates (diC(8)GE-E-n, where n = 4.6-15.8), were synthesized and characterized and the effects of the ethylene oxide (EO) number on their properties were evaluated. The results show that diC(8)GE-E-n, are highly surface-active, as reflected by their low critical micelle concentration (cmc) (<2 X 10(-5) mol/L) and low gamma(cmc) (<30 mN/m). Specifically, the member with the shortest EO chain (diC(8)GE-E-4.6), which gives a saturated adsorption (5.81 x 10(-10) mol/cm(2)) nearly double that of others (2.94-2.63 X 10(-18) mol/cm(2)) at the air/water interface, can reduce Daqing crude oil/connate water interfacial tension (IFT) to ultralow (<0.01 mN/m) solely at 5 mM at 45 degrees C. The members with larger EO numbers, although cannot reduce Daqing crude oil/connate water IFT to ultralow solely, are very good hydrophilic components superior to a typical monoalkyl non-ionic surfactant, such as polyoxyethylene (10) monododecyl ether (C12E10, when mixed with a hydrophobic surfactant, didodecyl methyl hydroxylpropyl sulfobetaine (diC(12)HSB), for SP flooding free of alkali. At optimum formulation, the molar fraction of diC(8)GE-E-n can be decreased from 0.85 to 0.45 with increasing n from 8.0 to 15.8 and ultralow IFT can be easily achieved at a wide effective concentration range (0.3-10 mM) thanks to the larger interaction of the double alkyl chains in the molecules with the oil. Derived from commercially available materials and produced by commercially realizable technology, these surfactants are therefore practically significant for SP flooding.