Purpose The purpose of this paper is to examine the effect of crude oil prices on the Nigerian exchange rate with emphasis on discriminating between the effects of positive and negative changes in oil price on exchange rate. Design/methodology/approach The authors used monthly time series data from 1996:1 to 2019:6 and adopted two oil price measures, namely, Brent crude and West Texas Intermediary prices. For analysis, the authors used stepwise least squares to estimate a non-linear ARDL (NARDL) model and Wald tests to determine cointegration and the presence of asymmetric effects. Findings The findings showed that positive and negative Brent crude price changes significantly affect exchange rates differently in nominal terms, both in the long-run and short-run. However, the differences were purely in terms of effect size because the exchange rate decreased for both negative and positive oil price changes. Originality/value Whilst empirical research on asymmetries in the effect of oil price on exchange rate abounds, little evidence exists in Nigeria’s case. Although some studies previously tested for asymmetric oil price effects on the Nigerian currency, the approach used did not estimate long and short-run effects or test of long-run and short-run asymmetries. This paper fills this methodological gap using monthly using the NARDL approach. The NARDL approach provided the advantage of estimating effects for the long-run and short-run and testing for asymmetries in both time spans.