We analyzed how fossil crude oils can be generated in short periods using the sea microalga, coccolithophore Emiliania huxleyi (Haptophyta), which was the most effective oil producer among eight microalgal species. Powdered E. huxleyi was pyrolyzed under various conditions, and then total dichloromethane-extractable (TDE)-fractions were prepared from the products. To evaluate the generation of crude oils in the pyrolysis products, we monitored the presence of SARA fractions comprising saturates, aromatics, resins, and asphaltenes, and n-alkanes of various chain lengths and their contents of polynuclear aromatic hydrocarbons (PAHs), which are a common feature of most fossil oils. After pyrolysis at 300 degrees C for 4-45 days, TDE-fractions derived from the products included charcoal and SARA fractions. Their GC-MS profiles revealed a high yield of various n-alkanes with carbon chains ranging from 12 to 35, which were similar to those in fossil oils, although they also contained more longer-chain n-alkanes (range, 28-35 carbon atoms) than those found in fossil oils. After pyrolysis of powdered E. huxleyi at 400 degrees C for 6 hours, no charcoal was extracted and the GC-MS profiles of the products were almost identical to those of fossil oils. The pyrolysis products contained 1-alkenes of various lengths that were similar to those of shale crude oils. High levels of PAHs were detected in products after pyrolysis at 510 degrees C. We prepared 0.8 g of n-alkane-rich oil by simply heating 10 g of E. huxleyi cells at 400 degrees C. The GC-MS and infrared spectrometry profiles of this oil, which was the hexane extract from the pyrolysis product, were identical to those of fossil crude oils.