Single-cell protein (SCP) was produced by utilization of Morgan gas-oil as the carbon source by Candida lipolytica YB-423. The chemical constituents of the gas oil SCP were compared with SCP produced by C. lipolytica YB-423 grown on yeast extract and malt extract (YM), Saccharomyces carlsbergensis grown on malt (obtained from the Al-Ahram Beer Company) and Sac. cerevisiae on molasses (obtained from the Egyptian Sugar and Distillation Company). The whole cells produced on gas-oil contained more crude protein (42%) and crude fat (6.98%) than the other SCP. The gas-oil cells were treated by different techniques to reduce the nucleic acid content. The most suitable technique was extraction of protein from yeast cells with sodium hydroxide, which increased the total protein (about 1.68 fold) in the product and removed about 75% of the RNA and 81% of the DNA. The protein-extract solubility was higher than that of the crude yeast cell, except at the highest pH values.