Listening effort refers to the use of working memory and/or attentional resources to understand speech. In the current study, it was hypothesized that electrophysiological measures of listening effort, specifically oscillatory power in the alpha (8–12 Hz) and theta (4–8 Hz) frequency bands, would be affected by signal-to-noise ratio (SNR), reflecting increased effort in more difficult listening conditions. Furthermore, changes in effort across trials were assessed as interactions with trial number. Although most studies of effects of aging on listening effort have compared young and older adults, impacts of aging on hearing and cognition begin in middle-age. Here, middle-aged adults (n = 11; age range = 37—65 years) with and without hearing loss listened to spoken sentences in a background of multi-talker babble at a range of SNRs relative to an individualized SNR corresponding to the speech recognition threshold. Each electrophysiological measure tracked with SNR, such that alpha power decreased for lower (poorer) SNRs, whereas theta power increased at lower SNRs. Notably, the linear effect of SNR on alpha power emerged only at later trials. Overall, results support use of these measures as neural markers of listening effort during speech perception in middle-aged adults but indicate that alpha power measures of listening effort may emerge gradually over an episode of listening, perhaps reflecting listening-related fatigue, in contrast to theta power effects, which may emerge more quickly.