Recent studies show that oil production from unconventional tight rocks is inefficient because oil is mainly trapped in their submicron hydrophobic pores. Different types of surfactants have been proposed to enhance the imbibition of aqueous fluids into such pore systems for enhanced oil recovery. The efficiency of this process strongly depends on surfactant's chemical structure and its interactions with oil and pore walls. This study aims at investigating the interactions between oil and nonionic octylphenol ethoxylate (OPE) surfactant solutions in narrow hydrophobic pores. We perform different sets of experiments to investigate how mixing OPE surfactants with long- and short-ethoxylate (EO) chains can enhance surfactant imbibition into hydrophobic pores to displace the residing oil. Interfacial tension values between the oil and mixed surfactants (with no synergetic interactions between them) are in the same range of those between the oil and single surfactants. However, mixing OPE70 (having long EO chains) with OPE15 (having short EO chains) leads to 30% additional oil recovery factor during spontaneous imbibition tests compared with that achieved with the single OPE70 solution. The results suggest that the relatively small self-assemblies formed in mixed OPE solutions (<120 nm) have higher solubility in oil compared with those in the single solutions. Therefore, the mixed solutions can spontaneously imbibe into the hydrophobic pores and displace the oil out.