Waste engine oil pollution is an endemic problem in African countries as waste oil is often discharged into the environment without adequate treatment because waste oil recycling facilities are not readily available. In this study, laboratory-based microcosms (natural attenuation, biostimulation, bioaugmentation and combined treatment of biostimulation-bioaugmentation) were set up with soils (from old hydrocarbon biopiles) spiked with waste engine oil and monitored for 3 months. Total petroleum hydrocarbon analysis showed that biostimulation and biostimulation-bioaugmentation accelerated hydrocarbon degradation with over 84% reduction (<10,000 mgkg-1) by week 8. It took another 2 weeks for other microcosms to get below this classification of low-level contaminated waste and landfill disposal level. The highest degradation rate of 92% was obtained in biostimulated-bioaugmented microcosms (week 10). However, by week 12, there were no significant differences in hydrocarbon levels in naturally attenuated and treated microcosms. 16S rRNA and ITS-based denaturing gradient gel electrophoresis profiling showed diverse bacterial and fungal communities with some dominant members belonging to hydrocarbon-degrading Proteobacteria, Ascomycetes and Basidiomycetes. This research has therefore shown that hydrocarbon-polluted soils possess substantial microbial hydrocarbon-degrading capacity which was successfully harnessed for degrading engine oil. In developing countries without recycling facilities but readily available hydrocarbon-contaminated soils, using such soils for ex situ monitored natural attenuation could be an effective, low-cost and environmentfriendly option for treating waste engine oil.