Links between social relationships and emotional well-being in old age are well documented, but little is known about daily life fluctuations in momentary affective experiences of the oldest-old while interacting with specific social partners. We examined associations between the presence of different types of social partners and moment-to-moment fluctuations in affect in the oldest-old, taking into account individual differences in gender, neuroticism, depressive symptoms, chronic health conditions, and loneliness. Participants (N = 74, M age = 88.7 years, range = 84-102 years, 68% women) provided self-reports concurrently on the presence of social partners and subjective affective states 6 times a day for each of 7 consecutive days (3,071 occasions, in total). Relative to being with other people, time spent alone was associated with lower positive affect in the oldest-old. Being with other family members and friends was associated with more positive affective experiences. Compared with men, women reported more negative affective experiences when they were with their spouses than when their spouses were not present. Individuals with more chronic health problems reported more negative affective experiences when they were with their spouses than not. Participants higher in neuroticism reported more positive affective experiences when they were with their friends, compared with times when their friends were not present. Finally, lonelier individuals reported more positive affective experiences when they were with their spouses than when they were not. These findings suggest that affective experience is a function of individual differences and the type of social partners oldest-old adults interact with in everyday life. We discuss how our findings can be generalized to oldest-olds of different marital statuses, taking into account the proportion of widows in our sample as well as measurement specifics.