TECHNOLOGY FOCUS - BIOLOGY - Preferred Components: The oleaginous yeast is Rhodotorula glutinis, Rhodotorula gracilis, Rhodotorula graminis, Lipomyces starkeyi, Lipomyces lipofer, Trigonopsis variabilis, Candida kefyr, Candida curvata, Candida lipolytica, Torulopsis sp., Pichia stipitis, Cryptococcus albidus, and/or Cryptococcus sp..    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process: In the process, the solid urban waste is used in a mixture with other materials including: primary and biological sludges produced in wastewater purification plants; residues and/or waste derived from agricultural and/or zootechnic activities; residues and/or waste derived from the agricultural and food industry; and/or residues and/or waste derived from agricultural processing, forestation and/or sylviculture. The solid urban waste, alone or mixed with other materials, is treated by subjecting it to a preliminary grinding or sizing process before subjecting to liquefaction. The liquefaction step is carried out at 150-350 degrees C, preferably 200-320 degrees C and at a pressure of 5-170 bar, preferably 15-115 bar for 5-240, preferably 15-90 minutes. In the process, the oily phase, the solid phase and the aqueous phase included in the mixture are separated by gravitational separation, filtration or centrifugation. The fermentation step is carried out in the presence of at least one oleaginous yeast, or at least one microbial consortium isolated from the aqueous phase obtained in the liquefaction step. The fermentation step is carried out at 20-40 degrees C, preferably 25-35 degrees C at a pH of 4.5-7.5, preferably 5-7 for 10-120 hours, preferably 24-100 hours. At the end of the fermentation step, the fermented biomass is subjected to a thickening treatment before being fed to the liquefaction step. Preferred Components: The solid urban waste is: an organic material derived from differentiated waste collection and/or undifferentiated solid urban waste; or mixture of the organic material with pruning and mowing refuse and/or agricultural residues. The solid urban waste has a water content of greater than or equal to 50 wt.%, preferably 55-80 wt.% with respect to the total weight of the solid urban waste. EXAMPLE - Wet organic fraction of solid urban waste (SUW) (500 g) was fed, with a suitable dosage system, into a stirred autoclave (1 l), where the dry weight of this fraction was 25 wt.% (125 g). After creating an inert atmosphere inside the autoclave by washing with nitrogen, the autoclave was rapidly heated to reach the internal temperature of 310 degrees C and was kept under stirring, for 4 hours, and observing that the pressure inside the autoclave reached the maximum pressure of 110 bar. The autoclave was then rapidly cooled up to 80 degrees C and the gaseous phase was separated (22.5 g (18 wt.% of the dry fraction of the initial SUW)). The reaction mixture thus obtained was separated, under heating, in a gravitational separator obtaining three phases including: an oily phase comprising bio-oil, once anhydrified, equal to 42 g (33.6 wt.% of the dry fraction); a solid phase comprising a solid residue equal to 18.7 g (15 wt.% of the dry fraction); and an aqueous phase equal to 417 g having a SUW content equal to 41.7 g (32 wt.% of the dry fraction). The above aqueous phase was used totally and without any dilution as growth medium in the subsequent fermentation step, where yeast extract (1 g/l) was added as vitamin source and the pH was adjusted to 6.5 by means of the addition of an aqueous solution of potassium hydroxide (0.1 M). The aqueous phase was subsequently fed to a fermentor having a working volume of 1 l and inoculated with a microbial consortium isolated from an aqueous phase coming from the liquefaction treatment of the SUW, maintained under stirring, in air, at room temperature for 10 days. The fermentation was carried out at 30 degrees C at 170 rpm. After 70 hours, the biomass was recovered by centrifugation (5000 rpm for 30 minutes) obtaining wet biomass (59.5 g) comprising cells (20 wt.%, dry weight of 11.9 g). The fermented biomass thus obtained was fed to the above stirred 1 l autoclave, together with an organic fraction (500 g) of solid urban waste, where the liquefaction was carried out under the same operating conditions. After analogous separation treatment, a further bio-oil (4.2 g) was obtained, which in total lead to the formation of bio-oil (46.2 g).