Old-age needs are multifaceted and require multiple support sources, yet caregiving roles for older Nigerians are largely shifted to adult children. However, the children also declining capacity to respond. The extent to which older adults access support from other sources remains under-researched. This study investigates the patterns and determinants of access to complementary supports among older adults in South-Western Nigeria, taking Oyo State as the case study. The study is cross-sectional and utilized primary data of 827 older adults aged ≥ 65 years selected using a multi-stage sampling design. Box plot was used to determine the patterns while multiple ordinary least square regression was used to predict the determinants of access to complementary support. Expressed in percentage, the median complementary support score of older adults in Oyo State was 30 (interquartile range [IQR] = 24) with a slightly higher score for men (median = 32, IQR = 24) compared to women (median = 28, IQR = 20). Access to complementary support was lower for the widow(er)s, the lower socioeconomic group and self-dependent older adults across genders, and for urban women with secondary/higher education compared to the otherwise groups. Increased access to complementary support was significantly associated with primary/no education (β = 4.365; p < 0.01 95% C.I. = 1.511-7.218), affiliation to Islamic/Traditional religion (β = 5.100; p < 0.001; 95% C.I. = 3.000-7.200), rich wealth status (β = 3.315; p < 0.05; 95% C.I. = 0.667-5.963) and depending on both self and children/family for income (β = 5.510; p < 0.05; 95% C.I. = 1.710-9.309) with some gender disparities. However, reduced complementary support was associated with ages 80 years or over (β = -3.649; p < 0.05; 95% C.I. = -6.460 - -0.838) and widowhood (β = -6.285; p < 0.001; 95% C.I. = -8.556 - -4.015). The study suggests the need for welfare plans among professional, social, and religious groups, institutionalised social support systems, and community engagement to escalate welfare support for older adults. It also recommends intensified attention on the more vulnerable groups, especially the widows, childless and lower socioeconomic groups.