The co-combustion of microalgae biomass with coal has the potential to significantly reduce CO emissions by eliminating expensive and carbon-emitting downstream processes. In this study, the utilization of microalgal biomass as a direct combustion fuel in co-firing industries and the screening of potential oleaginous strains of high calorific value was investigated. High-lipid accumulating mutants were selected from mutant mixtures based on cell density using differential sedimentation rates. Of the mutant strains obtained in the top phase of the separation medium, 72% showed a higher lipid content than the wild-type strain. One mutant strain exhibited a 57.3% enhanced lipid content and a 9.3% lower heating value (LHV), both indicators of direct combustion fuel performance, compared to the wild-type strain. Our findings indicate that sedimentation rate-based strain selection allows for the easy and rapid screening of high-lipid content algal strains for the use of microalgae as direct combustion fuels.