<p>Oil palm production has known negative effects on biodiversity. The conversion of native forests to oil palm causes local species extinctions, alters community composition, and reduces ecosystem function. Quantifying the extent of this conversion within sites of high conservation importance is crucial to identify conservation priorities, but such global data are currently lacking. Here, we quantify the extent of oil palm (derived from satellite remote sensing) in 3,025 Key Biodiversity Areas (KBAs), within the global region suitable for growing oil palm. KBAs are areas identified for global biodiversity importance, but which do not necessarily benefit from protection. We found that oil palm is present in 8% of these KBAs, with the majority (67%) of those containing palm oil located within Southeast Asia. Oil palm was more prevalent in accessible KBAs situated in lowland moist rainforest and mangrove, but extent was not correlated with protected area coverage. The proportional extent of oil palm was approximately five times greater outside KBAs compared to inside, a pattern potentially related to the greater proportional availability of suitable oil palm growing area outside KBAs. The best supported logistic regression model indicated oil palm was most prevelant in low altitude, accessible areas outside protected areas. Over 1,500 terrestrial vertebrate species which trigger KBA identification (species with restricted distributions or of conservation concern) have likely been affected by oil palm within these KBAs. Considering oil palm plantations are more extensive outside KBAs, these findings stress the importance of KBAs as refuges for threatened and range-restricted species. With oil palm production expected to continue expanding, our results suggest KBAs should be considered a high-priority network of sites which need conservation interventions to limit further growth of oil palm plantation within KBAs.</p>