Process for producing a motor fuel or burning fuel from vegetable material comprises the production of pure esters from glucidic vegetable materials or derivatives of these as starting material, and using at least one of these esters as a component in or as a substitute for at least part of the fuel.    A preferred process comprises:    (a) if necessary, depolymerising the vegetable material or glucide-containing derivatives by hydrolysis to decompose it down into its constituent monosaccharides;    (b) if necessary, treating the lignins to transform them into monosaccharides; and    (c) converting the monosaccharides formed into the desired pure esters.    Step (c) may be accomplished by fermentation with microorganisms selected e.g. from yeasts, fungi and bacteria which are capable of selective production of the desired ester, or step (c) may comprise the steps of:    (d) fermenting the monosaccharides produced in stages (a) and (b) with microorganisms selected e.g. from yeasts, fungi and bacteria which are capable of selectively producing a pure carboxylic acid or a pure alcohol; and    (e) esterifying the acid or alcohol produced to form the desired pure ester.    Preferred microorganisms for producing 1-6 C acids are selected from Acetobacter, Clostridium thermoaceticum, Clostridium propionicum, Clostridium butyricum, Clostridium sp. or Clostridium kluyveri. Saccharomyces cerevisae, Pichia stipitis, Candida sp., Clostridium acetobutylicum, Zymomonas mobilis and Aspergillus flavus.    USE -   For conversion of vegetable material such as beet juice, molasses, cereal grains, straw, forestry waste, fresh urban vegetation, waste paper and cardboard and/or vegetable waste from the agricultural industry or domestic refuse, into a product useful as fuel. Saturated 3-6 C esters obtained in the process are added e.g. in amounts of 1-100 (5-33) wt. % to petroleum motor fuels; 7-20 C saturated or unsaturated esters are used in amounts of 1-100 (5-33) wt. % as an additive to or a substitute for gas oil or combustion fuel.    ADVANTAGE -   The ester products can be produced in selected chain lengths and can be added to the fuel of conventional engines, boilers, etc. without modification of the equipment. The esters can be obtained from locally available sources, are free from heavy metals and sulphur to give a cleaner burn, and cause less noxious emissions than equivalent petroleum based materials.